diff --git a/.travis.yml b/.travis.yml
index c4efa88460325..db1cfdc6ab2da 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -213,6 +213,10 @@ before_install:
 install:
   - case "$TRAVIS_OS_NAME" in
         linux)
+          $HOME/.nvm/nvm.sh &&
+            nvm install stable &&
+            nvm use stable &&
+            npm install eslint;
           travis_retry curl -fo $HOME/stamp https://s3-us-west-1.amazonaws.com/rust-lang-ci2/rust-ci-mirror/2017-03-17-stamp-x86_64-unknown-linux-musl &&
             chmod +x $HOME/stamp &&
             export PATH=$PATH:$HOME
diff --git a/config.toml.example b/config.toml.example
index f75e220de47e7..236d18dda8eb0 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -144,6 +144,10 @@
 # target when running tests, otherwise this can be omitted.
 #nodejs = "node"
 
+# The eslint executable to use. Note that this is only used for linting js files
+# during the test phase. It can be omitted.
+#eslint = "eslint"
+
 # Python interpreter to use for various tasks throughout the build, notably
 # rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
 # Note that Python 2 is currently required.
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 8655cf0eb3053..872cd200266eb 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -136,6 +136,7 @@ pub struct Config {
     pub libdir: Option<PathBuf>,
     pub mandir: Option<PathBuf>,
     pub codegen_tests: bool,
+    pub eslint: Option<PathBuf>,
     pub nodejs: Option<PathBuf>,
     pub gdb: Option<PathBuf>,
     pub python: Option<PathBuf>,
@@ -202,6 +203,7 @@ struct Build {
     gdb: Option<String>,
     locked_deps: Option<bool>,
     vendor: Option<bool>,
+    eslint: Option<String>,
     nodejs: Option<String>,
     python: Option<String>,
     full_bootstrap: Option<bool>,
@@ -444,6 +446,7 @@ impl Config {
         };
 
 
+        config.eslint = build.eslint.map(PathBuf::from);
         config.nodejs = build.nodejs.map(PathBuf::from);
         config.gdb = build.gdb.map(PathBuf::from);
         config.python = build.python.map(PathBuf::from);
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 2edc78ebaa94f..7ef6e104f4733 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -609,6 +609,14 @@ impl Step for RustdocJS {
                 "No nodejs found, skipping \"src/test/rustdoc-js\" tests"
             );
         }
+
+        if let Some(ref eslint) = builder.config.eslint {
+            let mut command = Command::new(eslint);
+            command.args(&["src/librustdoc/html/static"]);
+            builder.run(&mut command);
+        } else {
+            builder.info("No eslint found, skipping js linting");
+        }
     }
 }
 
diff --git a/src/librustdoc/html/static/.eslintrc.js b/src/librustdoc/html/static/.eslintrc.js
index c7af41ac969ce..3e1114f9c9ce8 100644
--- a/src/librustdoc/html/static/.eslintrc.js
+++ b/src/librustdoc/html/static/.eslintrc.js
@@ -6,7 +6,7 @@ module.exports = {
     "extends": "eslint:recommended",
     "parserOptions": {
         "ecmaVersion": 2015,
-        "sourceType": "module"
+        "sourceType": "script"
     },
     "rules": {
         "linebreak-style": [
@@ -16,6 +16,10 @@ module.exports = {
         "semi": [
             "error",
             "always"
+        ],
+        "no-constant-condition": [
+            "error",
+            { "checkLoops": false }
         ]
     }
 };
diff --git a/src/librustdoc/html/static/main.js b/src/librustdoc/html/static/main.js
index 75b0f5df0d8b3..e376462d6e3cf 100644
--- a/src/librustdoc/html/static/main.js
+++ b/src/librustdoc/html/static/main.js
@@ -1,9 +1,12 @@
 // From rust:
 /* global ALIASES, currentCrate, rootPath */
 
+// From DOM global ids:
+/* global help */
+
 // Local js definitions:
 /* global addClass, getCurrentValue, hasClass */
-/* global isHidden onEach, removeClass, updateLocalStorage */
+/* global isHidden, onEachLazy, removeClass, updateLocalStorage */
 
 if (!String.prototype.startsWith) {
     String.prototype.startsWith = function(searchString, position) {
@@ -13,7 +16,7 @@ if (!String.prototype.startsWith) {
 }
 if (!String.prototype.endsWith) {
     String.prototype.endsWith = function(suffix, length) {
-        var l = length || this.length;
+        let l = length || this.length;
         return this.indexOf(suffix, l - suffix.length) !== -1;
     };
 }
@@ -44,7 +47,7 @@ if (!DOMTokenList.prototype.remove) {
 
     // This mapping table should match the discriminants of
     // `rustdoc::html::item_type::ItemType` type in Rust.
-    var itemTypes = ["mod",
+    let itemTypes = ["mod",
                      "externcrate",
                      "import",
                      "struct",
@@ -70,21 +73,19 @@ if (!DOMTokenList.prototype.remove) {
                      "attr",
                      "derive"];
 
-    var search_input = document.getElementsByClassName("search-input")[0];
+    let search_input = document.getElementsByClassName("search-input")[0];
 
     // On the search screen, so you remain on the last tab you opened.
     //
     // 0 for "In Names"
     // 1 for "In Parameters"
     // 2 for "In Return Types"
-    var currentTab = 0;
-
-    var themesWidth = null;
+    let currentTab = 0;
 
-    var titleBeforeSearch = document.title;
+    let titleBeforeSearch = document.title;
 
     function getPageId() {
-        var id = document.location.href.split("#")[1];
+        let id = document.location.href.split("#")[1];
         if (id) {
             return id.split("?")[0].split("&")[0];
         }
@@ -92,57 +93,57 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function showSidebar() {
-        var elems = document.getElementsByClassName("sidebar-elems")[0];
+        let elems = document.getElementsByClassName("sidebar-elems")[0];
         if (elems) {
             addClass(elems, "show-it");
         }
-        var sidebar = document.getElementsByClassName("sidebar")[0];
+        let sidebar = document.getElementsByClassName("sidebar")[0];
         if (sidebar) {
             addClass(sidebar, "mobile");
-            var filler = document.getElementById("sidebar-filler");
+            let filler = document.getElementById("sidebar-filler");
             if (!filler) {
-                var div = document.createElement("div");
+                let div = document.createElement("div");
                 div.id = "sidebar-filler";
                 sidebar.appendChild(div);
             }
         }
-        var themePicker = document.getElementsByClassName("theme-picker");
+        let themePicker = document.getElementsByClassName("theme-picker");
         if (themePicker && themePicker.length > 0) {
             themePicker[0].style.display = "none";
         }
     }
 
     function hideSidebar() {
-        var elems = document.getElementsByClassName("sidebar-elems")[0];
+        let elems = document.getElementsByClassName("sidebar-elems")[0];
         if (elems) {
             removeClass(elems, "show-it");
         }
-        var sidebar = document.getElementsByClassName("sidebar")[0];
+        let sidebar = document.getElementsByClassName("sidebar")[0];
         removeClass(sidebar, "mobile");
-        var filler = document.getElementById("sidebar-filler");
+        let filler = document.getElementById("sidebar-filler");
         if (filler) {
             filler.remove();
         }
         document.getElementsByTagName("body")[0].style.marginTop = "";
-        var themePicker = document.getElementsByClassName("theme-picker");
+        let themePicker = document.getElementsByClassName("theme-picker");
         if (themePicker && themePicker.length > 0) {
             themePicker[0].style.display = null;
         }
     }
 
     // used for special search precedence
-    var TY_PRIMITIVE = itemTypes.indexOf("primitive");
-    var TY_KEYWORD = itemTypes.indexOf("keyword");
+    let TY_PRIMITIVE = itemTypes.indexOf("primitive");
+    let TY_KEYWORD = itemTypes.indexOf("keyword");
 
     onEachLazy(document.getElementsByClassName("js-only"), function(e) {
         removeClass(e, "js-only");
     });
 
     function getQueryStringParams() {
-        var params = {};
+        let params = {};
         window.location.search.substring(1).split("&").
             map(function(s) {
-                var pair = s.split("=");
+                let pair = s.split("=");
                 params[decodeURIComponent(pair[0])] =
                     typeof pair[1] === "undefined" ? null : decodeURIComponent(pair[1]);
             });
@@ -154,14 +155,14 @@ if (!DOMTokenList.prototype.remove) {
           window.history && typeof window.history.pushState === "function";
     }
 
-    var main = document.getElementById("main");
+    let main = document.getElementById("main");
 
     function highlightSourceLines(ev) {
         // If we're in mobile mode, we should add the sidebar in any case.
         hideSidebar();
-        var elem;
-        var search = document.getElementById("search");
-        var i, from, to, match = window.location.hash.match(/^#?(\d+)(?:-(\d+))?$/);
+        let elem;
+        let search = document.getElementById("search");
+        let i, from, to, match = window.location.hash.match(/^#?(\d+)(?:-(\d+))?$/);
         if (match) {
             from = parseInt(match[1], 10);
             to = Math.min(50000, parseInt(match[2] || match[1], 10));
@@ -171,7 +172,7 @@ if (!DOMTokenList.prototype.remove) {
                 return;
             }
             if (ev === null) {
-                var x = document.getElementById(from);
+                let x = document.getElementById(from);
                 if (x) {
                     x.scrollIntoView();
                 }
@@ -187,7 +188,7 @@ if (!DOMTokenList.prototype.remove) {
         } else if (ev !== null && search && !hasClass(search, "hidden") && ev.newURL) {
             addClass(search, "hidden");
             removeClass(main, "hidden");
-            var hash = ev.newURL.slice(ev.newURL.indexOf("#") + 1);
+            let hash = ev.newURL.slice(ev.newURL.indexOf("#") + 1);
             if (browserSupportsHistoryApi()) {
                 history.replaceState(hash, "", "?search=#" + hash);
             }
@@ -199,15 +200,15 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function expandSection(id) {
-        var elem = document.getElementById(id);
+        let elem = document.getElementById(id);
         if (elem && isHidden(elem)) {
-            var h3 = elem.parentNode.previousElementSibling;
+            let h3 = elem.parentNode.previousElementSibling;
             if (h3 && h3.tagName !== "H3") {
                 h3 = h3.previousElementSibling; // skip div.docblock
             }
 
             if (h3) {
-                var collapses = h3.getElementsByClassName("collapse-toggle");
+                let collapses = h3.getElementsByClassName("collapse-toggle");
                 if (collapses.length > 0) {
                     // The element is not visible, we need to make it appear!
                     collapseDocs(collapses[0], "show");
@@ -234,7 +235,7 @@ if (!DOMTokenList.prototype.remove) {
             return ev.key;
         }
 
-        var c = ev.charCode || ev.keyCode;
+        let c = ev.charCode || ev.keyCode;
         if (c == 27) {
             return "Escape";
         }
@@ -257,7 +258,7 @@ if (!DOMTokenList.prototype.remove) {
 
     function handleEscape(ev, help) {
         hideModal();
-        var search = document.getElementById("search");
+        let search = document.getElementById("search");
         if (hasClass(help, "hidden") === false) {
             displayHelp(false, ev);
         } else if (hasClass(search, "hidden") === false) {
@@ -275,7 +276,7 @@ if (!DOMTokenList.prototype.remove) {
             return;
         }
 
-        var help = document.getElementById("help");
+        let help = document.getElementById("help");
         if (document.activeElement.tagName === "INPUT") {
             switch (getVirtualKey(ev)) {
             case "Escape":
@@ -330,9 +331,9 @@ if (!DOMTokenList.prototype.remove) {
         } else if (hasClass(ev.target.parentNode, "collapse-toggle")) {
             collapseDocs(ev.target.parentNode, "toggle");
         } else if (ev.target.tagName === "SPAN" && hasClass(ev.target.parentNode, "line-numbers")) {
-            var prev_id = 0;
+            let prev_id = 0;
 
-            var set_fragment = function(name) {
+            let set_fragment = function(name) {
                 if (browserSupportsHistoryApi()) {
                     history.replaceState(null, null, "#" + name);
                     window.hashchange();
@@ -341,11 +342,11 @@ if (!DOMTokenList.prototype.remove) {
                 }
             };
 
-            var cur_id = parseInt(ev.target.id, 10);
+            let cur_id = parseInt(ev.target.id, 10);
 
             if (ev.shiftKey && prev_id) {
                 if (prev_id > cur_id) {
-                    var tmp = prev_id;
+                    let tmp = prev_id;
                     prev_id = cur_id;
                     cur_id = tmp;
                 }
@@ -362,23 +363,23 @@ if (!DOMTokenList.prototype.remove) {
         } else {
             // Making a collapsed element visible on onhashchange seems
             // too late
-            var a = findParentElement(ev.target, "A");
+            let a = findParentElement(ev.target, "A");
             if (a && a.hash) {
                 expandSection(a.hash.replace(/^#/, ""));
             }
         }
     };
 
-    var x = document.getElementsByClassName("version-selector");
+    let x = document.getElementsByClassName("version-selector");
     if (x.length > 0) {
         x[0].onchange = function() {
-            var i, match,
+            let i, match,
                 url = document.location.href,
                 stripped = "",
                 len = rootPath.match(/\.\.\//g).length + 1;
 
             for (i = 0; i < len; ++i) {
-                match = url.match(/\/[^\/]*$/);
+                match = url.match(/\/[^/]*$/);
                 if (i < len - 1) {
                     stripped = match[0] + stripped;
                 }
@@ -398,14 +399,14 @@ if (!DOMTokenList.prototype.remove) {
      * This code is an unmodified version of the code written by Marco de Wit
      * and was found at http://stackoverflow.com/a/18514751/745719
      */
-    var levenshtein_row2 = [];
+    let levenshtein_row2 = [];
     function levenshtein(s1, s2) {
         if (s1 === s2) {
             return 0;
         }
-        var s1_len = s1.length, s2_len = s2.length;
+        let s1_len = s1.length, s2_len = s2.length;
         if (s1_len && s2_len) {
-            var i1 = 0, i2 = 0, a, b, c, c2, row = levenshtein_row2;
+            let i1 = 0, i2 = 0, a, b, c, c2, row = levenshtein_row2;
             while (i1 < s1_len) {
                 row[i1] = ++i1;
             }
@@ -427,14 +428,14 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function initSearch(rawSearchIndex) {
-        var currentResults, index, searchIndex;
-        var MAX_LEV_DISTANCE = 3;
-        var MAX_RESULTS = 200;
-        var GENERICS_DATA = 1;
-        var NAME = 0;
-        var INPUTS_DATA = 0;
-        var OUTPUT_DATA = 1;
-        var params = getQueryStringParams();
+        let currentResults, index, searchIndex;
+        let MAX_LEV_DISTANCE = 3;
+        let MAX_RESULTS = 200;
+        let GENERICS_DATA = 1;
+        let NAME = 0;
+        let INPUTS_DATA = 0;
+        let OUTPUT_DATA = 1;
+        let params = getQueryStringParams();
 
         // Populate search bar with query string search term when provided,
         // but only if the input bar is empty. This avoid the obnoxious issue
@@ -454,8 +455,8 @@ if (!DOMTokenList.prototype.remove) {
          */
         function execQuery(query, searchWords, filterCrates) {
             function itemTypeFromName(typename) {
-                var length = itemTypes.length;
-                for (var i = 0; i < length; ++i) {
+                let length = itemTypes.length;
+                for (let i = 0; i < length; ++i) {
                     if (itemTypes[i] === typename) {
                         return i;
                     }
@@ -463,14 +464,14 @@ if (!DOMTokenList.prototype.remove) {
                 return -1;
             }
 
-            var valLower = query.query.toLowerCase(),
+            let valLower = query.query.toLowerCase(),
                 val = valLower,
                 typeFilter = itemTypeFromName(query.type),
                 results = {}, results_in_args = {}, results_returned = {},
                 split = valLower.split("::");
 
-            var length = split.length;
-            for (var z = 0; z < length; ++z) {
+            let length = split.length;
+            for (let z = 0; z < length; ++z) {
                 if (split[z] === "") {
                     split.splice(z, 1);
                     z -= 1;
@@ -478,14 +479,14 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             function transformResults(results, isType) {
-                var out = [];
-                var length = results.length;
-                for (var i = 0; i < length; ++i) {
+                let out = [];
+                let length = results.length;
+                for (let i = 0; i < length; ++i) {
                     if (results[i].id > -1) {
-                        var obj = searchIndex[results[i].id];
+                        let obj = searchIndex[results[i].id];
                         obj.lev = results[i].lev;
                         if (isType !== true || obj.type) {
-                            var res = buildHrefAndPath(obj);
+                            let res = buildHrefAndPath(obj);
                             obj.displayPath = pathSplitter(res[0]);
                             obj.fullPath = obj.displayPath + obj.name;
                             // To be sure than it some items aren't considered as duplicate.
@@ -502,15 +503,15 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             function sortResults(results, isType) {
-                var ar = [];
-                for (var entry in results) {
+                let ar = [];
+                for (let entry in results) {
                     if (results.hasOwnProperty(entry)) {
                         ar.push(results[entry]);
                     }
                 }
                 results = ar;
-                var i;
-                var nresults = results.length;
+                let i;
+                let nresults = results.length;
                 for (i = 0; i < nresults; ++i) {
                     results[i].word = searchWords[results[i].id];
                     results[i].item = searchIndex[results[i].id] || {};
@@ -521,7 +522,7 @@ if (!DOMTokenList.prototype.remove) {
                 }
 
                 results.sort(function(aaa, bbb) {
-                    var a, b;
+                    let a, b;
 
                     // Sort by non levenshtein results and then levenshtein results by the distance
                     // (less changes required to match means higher rankings)
@@ -587,15 +588,15 @@ if (!DOMTokenList.prototype.remove) {
                     return 0;
                 });
 
-                var length = results.length;
+                let length = results.length;
                 for (i = 0; i < length; ++i) {
-                    var result = results[i];
+                    let result = results[i];
 
                     // this validation does not make sense when searching by types
                     if (result.dontValidate) {
                         continue;
                     }
-                    var name = result.item.name.toLowerCase(),
+                    let name = result.item.name.toLowerCase(),
                         path = result.item.path.toLowerCase(),
                         parent = result.item.parent;
 
@@ -611,7 +612,7 @@ if (!DOMTokenList.prototype.remove) {
             function extractGenerics(val) {
                 val = val.toLowerCase();
                 if (val.indexOf("<") !== -1) {
-                    var values = val.substring(val.indexOf("<") + 1, val.lastIndexOf(">"));
+                    let values = val.substring(val.indexOf("<") + 1, val.lastIndexOf(">"));
                     return {
                         name: val.substring(0, val.indexOf("<")),
                         generics: values.split(/\s*,\s*/),
@@ -626,21 +627,19 @@ if (!DOMTokenList.prototype.remove) {
             function checkGenerics(obj, val) {
                 // The names match, but we need to be sure that all generics kinda
                 // match as well.
-                var lev_distance = MAX_LEV_DISTANCE + 1;
+                let lev_distance = MAX_LEV_DISTANCE + 1;
                 if (val.generics.length > 0) {
                     if (obj.length > GENERICS_DATA &&
                           obj[GENERICS_DATA].length >= val.generics.length) {
-                        var elems = obj[GENERICS_DATA].slice(0);
-                        var total = 0;
-                        var done = 0;
+                        let elems = obj[GENERICS_DATA].slice(0);
                         // We need to find the type that matches the most to remove it in order
                         // to move forward.
-                        var vlength = val.generics.length;
-                        for (var y = 0; y < vlength; ++y) {
-                            var lev = { pos: -1, lev: MAX_LEV_DISTANCE + 1};
-                            var elength = elems.length;
-                            for (var x = 0; x < elength; ++x) {
-                                var tmp_lev = levenshtein(elems[x], val.generics[y]);
+                        let vlength = val.generics.length;
+                        for (let y = 0; y < vlength; ++y) {
+                            let lev = { pos: -1, lev: MAX_LEV_DISTANCE + 1};
+                            let elength = elems.length;
+                            for (let x = 0; x < elength; ++x) {
+                                let tmp_lev = levenshtein(elems[x], val.generics[y]);
                                 if (tmp_lev < lev.lev) {
                                     lev.lev = tmp_lev;
                                     lev.pos = x;
@@ -649,8 +648,6 @@ if (!DOMTokenList.prototype.remove) {
                             if (lev.pos !== -1) {
                                 elems.splice(lev.pos, 1);
                                 lev_distance = Math.min(lev.lev, lev_distance);
-                                total += lev.lev;
-                                done += 1;
                             } else {
                                 return MAX_LEV_DISTANCE + 1;
                             }
@@ -663,17 +660,17 @@ if (!DOMTokenList.prototype.remove) {
 
             // Check for type name and type generics (if any).
             function checkType(obj, val, literalSearch) {
-                var lev_distance = MAX_LEV_DISTANCE + 1;
-                var x;
+                let lev_distance = MAX_LEV_DISTANCE + 1;
+                let x;
                 if (obj[NAME] === val.name) {
                     if (literalSearch === true) {
                         if (val.generics && val.generics.length !== 0) {
                             if (obj.length > GENERICS_DATA &&
                                   obj[GENERICS_DATA].length >= val.generics.length) {
-                                var elems = obj[GENERICS_DATA].slice(0);
-                                var allFound = true;
+                                let elems = obj[GENERICS_DATA].slice(0);
+                                let allFound = true;
 
-                                for (var y = 0; allFound === true && y < val.generics.length; ++y) {
+                                for (let y = 0; allFound === true && y < val.generics.length; ++y) {
                                     allFound = false;
                                     for (x = 0; allFound === false && x < elems.length; ++x) {
                                         allFound = elems[x] === val.generics[y];
@@ -694,7 +691,7 @@ if (!DOMTokenList.prototype.remove) {
                     // If the type has generics but don't match, then it won't return at this point.
                     // Otherwise, `checkGenerics` will return 0 and it'll return.
                     if (obj.length > GENERICS_DATA && obj[GENERICS_DATA].length !== 0) {
-                        var tmp_lev = checkGenerics(obj, val);
+                        let tmp_lev = checkGenerics(obj, val);
                         if (tmp_lev <= MAX_LEV_DISTANCE) {
                             return tmp_lev;
                         }
@@ -705,7 +702,7 @@ if (!DOMTokenList.prototype.remove) {
                 // Names didn't match so let's check if one of the generic types could.
                 if (literalSearch === true) {
                      if (obj.length > GENERICS_DATA && obj[GENERICS_DATA].length > 0) {
-                        var length = obj[GENERICS_DATA].length;
+                        let length = obj[GENERICS_DATA].length;
                         for (x = 0; x < length; ++x) {
                             if (obj[GENERICS_DATA][x] === val.name) {
                                 return true;
@@ -719,7 +716,7 @@ if (!DOMTokenList.prototype.remove) {
                     lev_distance = Math.min(checkGenerics(obj, val), lev_distance);
                 } else if (obj.length > GENERICS_DATA && obj[GENERICS_DATA].length > 0) {
                     // We can check if the type we're looking for is inside the generics!
-                    var olength = obj[GENERICS_DATA].length;
+                    let olength = obj[GENERICS_DATA].length;
                     for (x = 0; x < olength; ++x) {
                         lev_distance = Math.min(levenshtein(obj[GENERICS_DATA][x], val.name),
                                                 lev_distance);
@@ -731,13 +728,13 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             function findArg(obj, val, literalSearch) {
-                var lev_distance = MAX_LEV_DISTANCE + 1;
+                let lev_distance = MAX_LEV_DISTANCE + 1;
 
                 if (obj && obj.type && obj.type[INPUTS_DATA] &&
                       obj.type[INPUTS_DATA].length > 0) {
-                    var length = obj.type[INPUTS_DATA].length;
-                    for (var i = 0; i < length; i++) {
-                        var tmp = checkType(obj.type[INPUTS_DATA][i], val, literalSearch);
+                    let length = obj.type[INPUTS_DATA].length;
+                    for (let i = 0; i < length; i++) {
+                        let tmp = checkType(obj.type[INPUTS_DATA][i], val, literalSearch);
                         if (literalSearch === true && tmp === true) {
                             return true;
                         }
@@ -751,10 +748,10 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             function checkReturned(obj, val, literalSearch) {
-                var lev_distance = MAX_LEV_DISTANCE + 1;
+                let lev_distance = MAX_LEV_DISTANCE + 1;
 
                 if (obj && obj.type && obj.type.length > OUTPUT_DATA) {
-                    var tmp = checkType(obj.type[OUTPUT_DATA], val, literalSearch);
+                    let tmp = checkType(obj.type[OUTPUT_DATA], val, literalSearch);
                     if (literalSearch === true && tmp === true) {
                         return true;
                     }
@@ -770,26 +767,26 @@ if (!DOMTokenList.prototype.remove) {
                 if (contains.length === 0) {
                     return 0;
                 }
-                var ret_lev = MAX_LEV_DISTANCE + 1;
-                var path = ty.path.split("::");
+                let ret_lev = MAX_LEV_DISTANCE + 1;
+                let path = ty.path.split("::");
 
                 if (ty.parent && ty.parent.name) {
                     path.push(ty.parent.name.toLowerCase());
                 }
 
-                var length = path.length;
-                var clength = contains.length;
+                let length = path.length;
+                let clength = contains.length;
                 if (clength > length) {
                     return MAX_LEV_DISTANCE + 1;
                 }
-                for (var i = 0; i < length; ++i) {
+                for (let i = 0; i < length; ++i) {
                     if (i + clength > length) {
                         break;
                     }
-                    var lev_total = 0;
-                    var aborted = false;
-                    for (var x = 0; x < clength; ++x) {
-                        var lev = levenshtein(path[i + x], contains[x]);
+                    let lev_total = 0;
+                    let aborted = false;
+                    for (let x = 0; x < clength; ++x) {
+                        let lev = levenshtein(path[i + x], contains[x]);
                         if (lev > MAX_LEV_DISTANCE) {
                             aborted = true;
                             break;
@@ -811,7 +808,7 @@ if (!DOMTokenList.prototype.remove) {
                 if (filter === type) return true;
 
                 // Match related items
-                var name = itemTypes[type];
+                let name = itemTypes[type];
                 switch (itemTypes[filter]) {
                     case "constant":
                         return (name == "associatedconstant");
@@ -833,12 +830,12 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             // quoted values mean literal search
-            var nSearchWords = searchWords.length;
-            var i;
-            var ty;
-            var fullId;
-            var returned;
-            var in_args;
+            let nSearchWords = searchWords.length;
+            let i;
+            let ty;
+            let fullId;
+            let returned;
+            let in_args;
             if ((val.charAt(0) === "\"" || val.charAt(0) === "'") &&
                 val.charAt(val.length - 1) === val.charAt(0))
             {
@@ -890,21 +887,21 @@ if (!DOMTokenList.prototype.remove) {
                 query.search = val;
             // searching by type
             } else if (val.search("->") > -1) {
-                var trimmer = function(s) { return s.trim(); };
-                var parts = val.split("->").map(trimmer);
-                var input = parts[0];
+                let trimmer = function(s) { return s.trim(); };
+                let parts = val.split("->").map(trimmer);
+                let input = parts[0];
                 // sort inputs so that order does not matter
-                var inputs = input.split(",").map(trimmer).sort();
+                let inputs = input.split(",").map(trimmer).sort();
                 for (i = 0; i < inputs.length; ++i) {
                     inputs[i] = extractGenerics(inputs[i]);
                 }
-                var output = extractGenerics(parts[1]);
+                let output = extractGenerics(parts[1]);
 
                 for (i = 0; i < nSearchWords; ++i) {
                     if (filterCrates !== undefined && searchIndex[i].crate !== filterCrates) {
                         continue;
                     }
-                    var type = searchIndex[i].type;
+                    let type = searchIndex[i].type;
                     ty = searchIndex[i];
                     if (!type) {
                         continue;
@@ -912,17 +909,16 @@ if (!DOMTokenList.prototype.remove) {
                     fullId = generateId(ty);
 
                     // allow searching for void (no output) functions as well
-                    var typeOutput = type.length > OUTPUT_DATA ? type[OUTPUT_DATA].name : "";
                     returned = checkReturned(ty, output, true);
                     if (output.name === "*" || returned === true) {
                         in_args = false;
-                        var module = false;
+                        let module = false;
 
                         if (input === "*") {
                             module = true;
                         } else {
-                            var allFound = true;
-                            for (var it = 0; allFound === true && it < inputs.length; it++) {
+                            let allFound = true;
+                            for (let it = 0; allFound === true && it < inputs.length; it++) {
                                 allFound = checkType(type, inputs[it], true);
                             }
                             in_args = allFound;
@@ -959,12 +955,12 @@ if (!DOMTokenList.prototype.remove) {
                 query.output = val;
                 query.search = val;
                 // gather matching search results up to a certain maximum
-                val = val.replace(/\_/g, "");
+                val = val.replace(/_/g, "");
 
-                var valGenerics = extractGenerics(val);
+                let valGenerics = extractGenerics(val);
 
-                var paths = valLower.split("::");
-                var j;
+                let paths = valLower.split("::");
+                let j;
                 for (j = 0; j < paths.length; ++j) {
                     if (paths[j] === "") {
                         paths.splice(j, 1);
@@ -972,17 +968,15 @@ if (!DOMTokenList.prototype.remove) {
                     }
                 }
                 val = paths[paths.length - 1];
-                var contains = paths.slice(0, paths.length > 1 ? paths.length - 1 : 1);
+                let contains = paths.slice(0, paths.length > 1 ? paths.length - 1 : 1);
 
                 for (j = 0; j < nSearchWords; ++j) {
-                    var lev;
-                    var lev_distance;
+                    let lev;
                     ty = searchIndex[j];
                     if (!ty || (filterCrates !== undefined && ty.crate !== filterCrates)) {
                         continue;
                     }
-                    var lev_distance;
-                    var lev_add = 0;
+                    let lev_add = 0;
                     if (paths.length > 1) {
                         lev = checkPath(contains, paths[paths.length - 1], ty);
                         if (lev > MAX_LEV_DISTANCE) {
@@ -994,7 +988,7 @@ if (!DOMTokenList.prototype.remove) {
 
                     returned = MAX_LEV_DISTANCE + 1;
                     in_args = MAX_LEV_DISTANCE + 1;
-                    var index = -1;
+                    let index = -1;
                     // we want lev results to go lower than others
                     lev = MAX_LEV_DISTANCE + 1;
                     fullId = generateId(ty);
@@ -1072,19 +1066,19 @@ if (!DOMTokenList.prototype.remove) {
                 }
             }
 
-            var ret = {
+            let ret = {
                 "in_args": sortResults(results_in_args, true),
                 "returned": sortResults(results_returned, true),
                 "others": sortResults(results),
             };
             if (ALIASES && ALIASES[window.currentCrate] &&
                     ALIASES[window.currentCrate][query.raw]) {
-                var aliases = ALIASES[window.currentCrate][query.raw];
+                let aliases = ALIASES[window.currentCrate][query.raw];
                 for (i = 0; i < aliases.length; ++i) {
                     aliases[i].is_alias = true;
                     aliases[i].alias = query.raw;
                     aliases[i].path = aliases[i].p;
-                    var res = buildHrefAndPath(aliases[i]);
+                    let res = buildHrefAndPath(aliases[i]);
                     aliases[i].displayPath = pathSplitter(res[0]);
                     aliases[i].fullPath = aliases[i].displayPath + aliases[i].name;
                     aliases[i].href = res[1];
@@ -1113,7 +1107,7 @@ if (!DOMTokenList.prototype.remove) {
          * @return {[boolean]}       [Whether the result is valid or not]
          */
         function validateResult(name, path, keys, parent) {
-            for (var i = 0; i < keys.length; ++i) {
+            for (let i = 0; i < keys.length; ++i) {
                 // each check is for validation so we negate the conditions and invalidate
                 if (!(
                     // check for an exact name match
@@ -1132,7 +1126,7 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function getQuery(raw) {
-            var matches, type, query;
+            let matches, type, query;
             query = raw;
 
             matches = query.match(/^(fn|mod|struct|enum|trait|type|const|macro)\s*:\s*/i);
@@ -1150,15 +1144,15 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function initSearchNav() {
-            var hoverTimeout;
+            let hoverTimeout;
 
-            var click_func = function(e) {
-                var el = e.target;
+            let click_func = function(e) {
+                let el = e.target;
                 // to retrieve the real "owner" of the event.
                 while (el.tagName !== "TR") {
                     el = el.parentNode;
                 }
-                var dst = e.target.getElementsByTagName("a");
+                let dst = e.target.getElementsByTagName("a");
                 if (dst.length < 1) {
                     return;
                 }
@@ -1169,8 +1163,8 @@ if (!DOMTokenList.prototype.remove) {
                     document.location.href = dst.href;
                 }
             };
-            var mouseover_func = function(e) {
-                var el = e.target;
+            let mouseover_func = function(e) {
+                let el = e.target;
                 // to retrieve the real "owner" of the event.
                 while (el.tagName !== "TR") {
                     el = el.parentNode;
@@ -1195,9 +1189,9 @@ if (!DOMTokenList.prototype.remove) {
             search_input.onkeydown = function(e) {
                 // "actives" references the currently highlighted item in each search tab.
                 // Each array in "actives" represents a tab.
-                var actives = [[], [], []];
+                let actives = [[], [], []];
                 // "current" is used to know which tab we're looking into.
-                var current = 0;
+                let current = 0;
                 onEachLazy(document.getElementsByClassName("search-results"), function(e) {
                     onEachLazy(e.getElementsByClassName("highlighted"), function(e) {
                         actives[current].push(e);
@@ -1215,9 +1209,9 @@ if (!DOMTokenList.prototype.remove) {
                     removeClass(actives[currentTab][0], "highlighted");
                 } else if (e.which === 40) { // down
                     if (!actives[currentTab].length) {
-                        var results = document.getElementsByClassName("search-results");
+                        let results = document.getElementsByClassName("search-results");
                         if (results.length > 0) {
-                            var res = results[currentTab].getElementsByClassName("result");
+                            let res = results[currentTab].getElementsByClassName("result");
                             if (res.length > 0) {
                                 addClass(res[0], "highlighted");
                             }
@@ -1251,10 +1245,10 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function buildHrefAndPath(item) {
-            var displayPath;
-            var href;
-            var type = itemTypes[item.ty];
-            var name = item.name;
+            let displayPath;
+            let href;
+            let type = itemTypes[item.ty];
+            let name = item.name;
 
             if (type === "mod") {
                 displayPath = item.path + "::";
@@ -1268,9 +1262,9 @@ if (!DOMTokenList.prototype.remove) {
                 displayPath = "";
                 href = rootPath + name + "/index.html";
             } else if (item.parent !== undefined) {
-                var myparent = item.parent;
-                var anchor = "#" + type + "." + name;
-                var parentType = itemTypes[myparent.ty];
+                let myparent = item.parent;
+                let anchor = "#" + type + "." + name;
+                let parentType = itemTypes[myparent.ty];
                 if (parentType === "primitive") {
                     displayPath = myparent.name + "::";
                 } else {
@@ -1289,13 +1283,13 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function escape(content) {
-            var h1 = document.createElement("h1");
+            let h1 = document.createElement("h1");
             h1.textContent = content;
             return h1.innerHTML;
         }
 
         function pathSplitter(path) {
-            var tmp = "<span>" + path.replace(/::/g, "::</span><span>");
+            let tmp = "<span>" + path.replace(/::/g, "::</span><span>");
             if (tmp.endsWith("<span>")) {
                 return tmp.slice(0, tmp.length - 6);
             }
@@ -1303,19 +1297,19 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function addTab(array, query, display) {
-            var extraStyle = "";
+            let extraStyle = "";
             if (display === false) {
                 extraStyle = " style=\"display: none;\"";
             }
 
-            var output = "";
-            var duplicates = {};
-            var length = 0;
+            let output = "";
+            let duplicates = {};
+            let length = 0;
             if (array.length > 0) {
                 output = "<table class=\"search-results\"" + extraStyle + ">";
 
                 array.forEach(function(item) {
-                    var name, type;
+                    let name, type;
 
                     name = item.name;
                     type = itemTypes[item.ty];
@@ -1369,22 +1363,22 @@ if (!DOMTokenList.prototype.remove) {
         function showResults(results) {
             if (results.others.length === 1 &&
                 getCurrentValue("rustdoc-go-to-only-result") === "true") {
-                var elem = document.createElement("a");
+                let elem = document.createElement("a");
                 elem.href = results.others[0].href;
                 elem.style.display = "none";
                 // For firefox, we need the element to be in the DOM so it can be clicked.
                 document.body.appendChild(elem);
                 elem.click();
             }
-            var query = getQuery(search_input.value);
+            let query = getQuery(search_input.value);
 
             currentResults = query.id;
 
-            var ret_others = addTab(results.others, query);
-            var ret_in_args = addTab(results.in_args, query, false);
-            var ret_returned = addTab(results.returned, query, false);
+            let ret_others = addTab(results.others, query);
+            let ret_in_args = addTab(results.in_args, query, false);
+            let ret_returned = addTab(results.returned, query, false);
 
-            var output = "<h1>Results for " + escape(query.query) +
+            let output = "<h1>Results for " + escape(query.query) +
                 (query.type ? " (type: " + escape(query.type) + ")" : "") + "</h1>" +
                 "<div id=\"titles\">" +
                 makeTabHeader(0, "In Names", ret_others[1]) +
@@ -1394,20 +1388,20 @@ if (!DOMTokenList.prototype.remove) {
                 ret_others[0] + ret_in_args[0] + ret_returned[0] + "</div>";
 
             addClass(main, "hidden");
-            var search = document.getElementById("search");
+            let search = document.getElementById("search");
             removeClass(search, "hidden");
             search.innerHTML = output;
-            var tds = search.getElementsByTagName("td");
-            var td_width = 0;
+            let tds = search.getElementsByTagName("td");
+            let td_width = 0;
             if (tds.length > 0) {
                 td_width = tds[0].offsetWidth;
             }
-            var width = search.offsetWidth - 40 - td_width;
+            let width = search.offsetWidth - 40 - td_width;
             onEachLazy(search.getElementsByClassName("desc"), function(e) {
                 e.style.width = width + "px";
             });
             initSearchNav();
-            var elems = document.getElementById("titles").childNodes;
+            let elems = document.getElementById("titles").childNodes;
             elems[0].onclick = function() { printTab(0); };
             elems[1].onclick = function() { printTab(1); };
             elems[2].onclick = function() { printTab(2); };
@@ -1416,9 +1410,9 @@ if (!DOMTokenList.prototype.remove) {
 
         function execSearch(query, searchWords, filterCrates) {
             function getSmallest(arrays, positions, notDuplicates) {
-                var start = null;
+                let start = null;
 
-                for (var it = 0; it < positions.length; ++it) {
+                for (let it = 0; it < positions.length; ++it) {
                     if (arrays[it].length > positions[it] &&
                         (start === null || start > arrays[it][positions[it]].lev) &&
                         !notDuplicates[arrays[it][positions[it]].fullPath]) {
@@ -1429,15 +1423,15 @@ if (!DOMTokenList.prototype.remove) {
             }
 
             function mergeArrays(arrays) {
-                var ret = [];
-                var positions = [];
-                var notDuplicates = {};
+                let ret = [];
+                let positions = [];
+                let notDuplicates = {};
 
-                for (var x = 0; x < arrays.length; ++x) {
+                for (let x = 0; x < arrays.length; ++x) {
                     positions.push(0);
                 }
                 while (ret.length < MAX_RESULTS) {
-                    var smallest = getSmallest(arrays, positions, notDuplicates);
+                    let smallest = getSmallest(arrays, positions, notDuplicates);
 
                     if (smallest === null) {
                         break;
@@ -1455,17 +1449,17 @@ if (!DOMTokenList.prototype.remove) {
                 return ret;
             }
 
-            var queries = query.raw.split(",");
-            var results = {
+            let queries = query.raw.split(",");
+            let results = {
                 "in_args": [],
                 "returned": [],
                 "others": [],
             };
 
-            for (var i = 0; i < queries.length; ++i) {
+            for (let i = 0; i < queries.length; ++i) {
                 query = queries[i].trim();
                 if (query.length !== 0) {
-                    var tmp = execQuery(getQuery(query), searchWords, filterCrates);
+                    let tmp = execQuery(getQuery(query), searchWords, filterCrates);
 
                     results.in_args.push(tmp.in_args);
                     results.returned.push(tmp.returned);
@@ -1488,7 +1482,7 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function getFilterCrates() {
-            var elem = document.getElementById("crate-search");
+            let elem = document.getElementById("crate-search");
 
             if (elem && elem.value !== "All crates" && rawSearchIndex.hasOwnProperty(elem.value)) {
                 return elem.value;
@@ -1497,8 +1491,8 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function search(e, forced) {
-            var params = getQueryStringParams();
-            var query = getQuery(search_input.value.trim());
+            let params = getQueryStringParams();
+            let query = getQuery(search_input.value.trim());
 
             if (e) {
                 e.preventDefault();
@@ -1527,16 +1521,16 @@ if (!DOMTokenList.prototype.remove) {
                 }
             }
 
-            var filterCrates = getFilterCrates();
+            let filterCrates = getFilterCrates();
             showResults(execSearch(query, index, filterCrates), filterCrates);
         }
 
         function buildIndex(rawSearchIndex) {
             searchIndex = [];
-            var searchWords = [];
-            var i;
+            let searchWords = [];
+            let i;
 
-            for (var crate in rawSearchIndex) {
+            for (let crate in rawSearchIndex) {
                 if (!rawSearchIndex.hasOwnProperty(crate)) { continue; }
 
                 searchWords.push(crate);
@@ -1555,13 +1549,13 @@ if (!DOMTokenList.prototype.remove) {
                 //              (String) description,
                 //              (Number | null) the parent path index to `paths`]
                 //              (Object | null) the type of the function (if any)
-                var items = rawSearchIndex[crate].items;
+                let items = rawSearchIndex[crate].items;
                 // an array of [(Number) item type,
                 //              (String) name]
-                var paths = rawSearchIndex[crate].paths;
+                let paths = rawSearchIndex[crate].paths;
 
                 // convert `paths` into an object form
-                var len = paths.length;
+                let len = paths.length;
                 for (i = 0; i < len; ++i) {
                     paths[i] = {ty: paths[i][0], name: paths[i][1]};
                 }
@@ -1574,15 +1568,15 @@ if (!DOMTokenList.prototype.remove) {
                 // all other search operations have access to this cached data for
                 // faster analysis operations
                 len = items.length;
-                var lastPath = "";
+                let lastPath = "";
                 for (i = 0; i < len; ++i) {
-                    var rawRow = items[i];
-                    var row = {crate: crate, ty: rawRow[0], name: rawRow[1],
+                    let rawRow = items[i];
+                    let row = {crate: crate, ty: rawRow[0], name: rawRow[1],
                                path: rawRow[2] || lastPath, desc: rawRow[3],
                                parent: paths[rawRow[4]], type: rawRow[5]};
                     searchIndex.push(row);
                     if (typeof row.name === "string") {
-                        var word = row.name.toLowerCase();
+                        let word = row.name.toLowerCase();
                         searchWords.push(word);
                     } else {
                         searchWords.push("");
@@ -1594,8 +1588,8 @@ if (!DOMTokenList.prototype.remove) {
         }
 
         function startSearch() {
-            var searchTimeout;
-            var callback = function() {
+            let searchTimeout;
+            let callback = function() {
                 clearTimeout(searchTimeout);
                 if (search_input.value.length === 0) {
                     if (browserSupportsHistoryApi()) {
@@ -1604,7 +1598,7 @@ if (!DOMTokenList.prototype.remove) {
                     if (hasClass(main, "content")) {
                         removeClass(main, "hidden");
                     }
-                    var search_c = document.getElementById("search");
+                    let search_c = document.getElementById("search");
                     if (hasClass(search_c, "content")) {
                         addClass(search_c, "hidden");
                     }
@@ -1619,7 +1613,7 @@ if (!DOMTokenList.prototype.remove) {
                 clearTimeout(searchTimeout);
                 search();
             };
-            search_input.onchange = function(e) {
+            search_input.onchange = function() {
                 // Do NOT e.preventDefault() here. It will prevent pasting.
                 clearTimeout(searchTimeout);
                 // zero-timeout necessary here because at the time of event handler execution the
@@ -1629,7 +1623,7 @@ if (!DOMTokenList.prototype.remove) {
             };
             search_input.onpaste = search_input.onchange;
 
-            var selectCrate = document.getElementById('crate-search');
+            let selectCrate = document.getElementById('crate-search');
             if (selectCrate) {
                 selectCrate.onchange = function() {
                     search(undefined, true);
@@ -1640,17 +1634,17 @@ if (!DOMTokenList.prototype.remove) {
             // history.
             if (browserSupportsHistoryApi()) {
                 // Store the previous <title> so we can revert back to it later.
-                var previousTitle = document.title;
+                let previousTitle = document.title;
 
-                window.onpopstate = function(e) {
-                    var params = getQueryStringParams();
+                window.onpopstate = function() {
+                    let params = getQueryStringParams();
                     // When browsing back from search results the main page
                     // visibility must be reset.
                     if (!params.search) {
                         if (hasClass(main, "content")) {
                             removeClass(main, "hidden");
                         }
-                        var search_c = document.getElementById("search");
+                        let search_c = document.getElementById("search");
                         if (hasClass(search_c, "content")) {
                             addClass(search_c, "hidden");
                         }
@@ -1687,34 +1681,34 @@ if (!DOMTokenList.prototype.remove) {
 
         // Draw a convenient sidebar of known crates if we have a listing
         if (rootPath === "../" || rootPath === "./") {
-            var sidebar = document.getElementsByClassName("sidebar-elems")[0];
+            let sidebar = document.getElementsByClassName("sidebar-elems")[0];
             if (sidebar) {
-                var div = document.createElement("div");
+                let div = document.createElement("div");
                 div.className = "block crate";
                 div.innerHTML = "<h3>Crates</h3>";
-                var ul = document.createElement("ul");
+                let ul = document.createElement("ul");
                 div.appendChild(ul);
 
-                var crates = [];
-                for (var crate in rawSearchIndex) {
+                let crates = [];
+                for (let crate in rawSearchIndex) {
                     if (!rawSearchIndex.hasOwnProperty(crate)) {
                         continue;
                     }
                     crates.push(crate);
                 }
                 crates.sort();
-                for (var i = 0; i < crates.length; ++i) {
-                    var klass = "crate";
+                for (let i = 0; i < crates.length; ++i) {
+                    let klass = "crate";
                     if (rootPath !== "./" && crates[i] === window.currentCrate) {
                         klass += " current";
                     }
-                    var link = document.createElement("a");
+                    let link = document.createElement("a");
                     link.href = rootPath + crates[i] + "/index.html";
                     link.title = rawSearchIndex[crates[i]].doc;
                     link.className = klass;
                     link.textContent = crates[i];
 
-                    var li = document.createElement("li");
+                    let li = document.createElement("li");
                     li.appendChild(link);
                     ul.appendChild(li);
                 }
@@ -1727,44 +1721,44 @@ if (!DOMTokenList.prototype.remove) {
 
     // delayed sidebar rendering.
     function initSidebarItems(items) {
-        var sidebar = document.getElementsByClassName("sidebar-elems")[0];
-        var current = window.sidebarCurrent;
+        let sidebar = document.getElementsByClassName("sidebar-elems")[0];
+        let current = window.sidebarCurrent;
 
         function block(shortty, longty) {
-            var filtered = items[shortty];
+            let filtered = items[shortty];
             if (!filtered) {
                 return;
             }
 
-            var div = document.createElement("div");
+            let div = document.createElement("div");
             div.className = "block " + shortty;
-            var h3 = document.createElement("h3");
+            let h3 = document.createElement("h3");
             h3.textContent = longty;
             div.appendChild(h3);
-            var ul = document.createElement("ul");
+            let ul = document.createElement("ul");
 
-            var length = filtered.length;
-            for (var i = 0; i < length; ++i) {
-                var item = filtered[i];
-                var name = item[0];
-                var desc = item[1]; // can be null
+            let length = filtered.length;
+            for (let i = 0; i < length; ++i) {
+                let item = filtered[i];
+                let name = item[0];
+                let desc = item[1]; // can be null
 
-                var klass = shortty;
+                let klass = shortty;
                 if (name === current.name && shortty === current.ty) {
                     klass += " current";
                 }
-                var path;
+                let path;
                 if (shortty === "mod") {
                     path = name + "/index.html";
                 } else {
                     path = shortty + "." + name + ".html";
                 }
-                var link = document.createElement("a");
+                let link = document.createElement("a");
                 link.href = current.relpath + path;
                 link.title = desc;
                 link.className = klass;
                 link.textContent = name;
-                var li = document.createElement("li");
+                let li = document.createElement("li");
                 li.appendChild(link);
                 ul.appendChild(li);
             }
@@ -1792,25 +1786,25 @@ if (!DOMTokenList.prototype.remove) {
     window.initSidebarItems = initSidebarItems;
 
     window.register_implementors = function(imp) {
-        var implementors = document.getElementById("implementors-list");
-        var synthetic_implementors = document.getElementById("synthetic-implementors-list");
+        let implementors = document.getElementById("implementors-list");
+        let synthetic_implementors = document.getElementById("synthetic-implementors-list");
 
-        var libs = Object.getOwnPropertyNames(imp);
-        var llength = libs.length;
-        for (var i = 0; i < llength; ++i) {
+        let libs = Object.getOwnPropertyNames(imp);
+        let llength = libs.length;
+        for (let i = 0; i < llength; ++i) {
             if (libs[i] === currentCrate) { continue; }
-            var structs = imp[libs[i]];
+            let structs = imp[libs[i]];
 
-            var slength = structs.length;
+            let slength = structs.length;
             struct_loop:
-            for (var j = 0; j < slength; ++j) {
-                var struct = structs[j];
+            for (let j = 0; j < slength; ++j) {
+                let struct = structs[j];
 
-                var list = struct.synthetic ? synthetic_implementors : implementors;
+                let list = struct.synthetic ? synthetic_implementors : implementors;
 
                 if (struct.synthetic) {
-                    var stlength = struct.types.length;
-                    for (var k = 0; k < stlength; k++) {
+                    let stlength = struct.types.length;
+                    for (let k = 0; k < stlength; k++) {
                         if (window.inlined_types.has(struct.types[k])) {
                             continue struct_loop;
                         }
@@ -1818,18 +1812,18 @@ if (!DOMTokenList.prototype.remove) {
                     }
                 }
 
-                var code = document.createElement("code");
+                let code = document.createElement("code");
                 code.innerHTML = struct.text;
 
-                var x = code.getElementsByTagName("a");
-                var xlength = x.length;
-                for (var it = 0; it < xlength; it++) {
-                    var href = x[it].getAttribute("href");
+                let x = code.getElementsByTagName("a");
+                let xlength = x.length;
+                for (let it = 0; it < xlength; it++) {
+                    let href = x[it].getAttribute("href");
                     if (href && href.indexOf("http") !== 0) {
                         x[it].setAttribute("href", rootPath + href);
                     }
                 }
-                var display = document.createElement("h3");
+                let display = document.createElement("h3");
                 addClass(display, "impl");
                 display.innerHTML = "<span class=\"in-band\"><table class=\"table-display\">" +
                     "<tbody><tr><td><code>" + code.outerHTML + "</code></td><td></td></tr>" +
@@ -1854,9 +1848,9 @@ if (!DOMTokenList.prototype.remove) {
 
     function onEveryMatchingChild(elem, className, func) {
         if (elem && className && func) {
-            var length = elem.childNodes.length;
-            var nodes = elem.childNodes;
-            for (var i = 0; i < length; ++i) {
+            let length = elem.childNodes.length;
+            let nodes = elem.childNodes;
+            for (let i = 0; i < length; ++i) {
                 if (hasClass(nodes[i], className)) {
                     func(nodes[i]);
                 } else {
@@ -1867,7 +1861,7 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function toggleAllDocs(pageId, fromAutoCollapse) {
-        var innerToggle = document.getElementById("toggle-all-docs");
+        let innerToggle = document.getElementById("toggle-all-docs");
         if (!innerToggle) {
             return;
         }
@@ -1920,7 +1914,7 @@ if (!DOMTokenList.prototype.remove) {
 
         function implHider(addOrRemove) {
             return function(n) {
-                var is_method = hasClass(n, "method");
+                let is_method = hasClass(n, "method");
                 if (is_method || hasClass(n, "type")) {
                     if (is_method === true) {
                         if (addOrRemove) {
@@ -1929,7 +1923,7 @@ if (!DOMTokenList.prototype.remove) {
                             removeClass(n, "hidden-by-impl-hider");
                         }
                     }
-                    var ns = n.nextElementSibling;
+                    let ns = n.nextElementSibling;
                     while (true) {
                         if (ns && (
                                 hasClass(ns, "docblock") ||
@@ -1948,8 +1942,8 @@ if (!DOMTokenList.prototype.remove) {
             };
         }
 
-        var relatedDoc;
-        var action = mode;
+        let relatedDoc;
+        let action = mode;
         if (hasClass(toggle.parentNode, "impl") === false) {
             relatedDoc = toggle.parentNode.nextElementSibling;
             if (hasClass(relatedDoc, "stability")) {
@@ -1976,9 +1970,9 @@ if (!DOMTokenList.prototype.remove) {
         } else {
             // we are collapsing the impl block
 
-            var parentElem = toggle.parentNode;
+            let parentElem = toggle.parentNode;
             relatedDoc = parentElem;
-            var docblock = relatedDoc.nextElementSibling;
+            let docblock = relatedDoc.nextElementSibling;
 
             while (hasClass(relatedDoc, "impl-items") === false) {
                 relatedDoc = relatedDoc.nextElementSibling;
@@ -2017,7 +2011,7 @@ if (!DOMTokenList.prototype.remove) {
     function collapser(e, collapse) {
         // inherent impl ids are like "impl" or impl-<number>'.
         // they will never be hidden by default.
-        var n = e.parentElement;
+        let n = e.parentElement;
         if (n.id.match(/^impl(?:-\d+)?$/) === null) {
             // Automatically minimize all non-inherent impls
             if (collapse || hasClass(n, "impl")) {
@@ -2030,7 +2024,7 @@ if (!DOMTokenList.prototype.remove) {
         if (collapse) {
             toggleAllDocs(pageId, true);
         } else if (getCurrentValue("rustdoc-trait-implementations") !== "false") {
-            var impl_list = document.getElementById("implementations-list");
+            let impl_list = document.getElementById("implementations-list");
 
             if (impl_list !== null) {
                 onEachLazy(impl_list.getElementsByClassName("collapse-toggle"), function(e) {
@@ -2040,7 +2034,7 @@ if (!DOMTokenList.prototype.remove) {
         }
     }
 
-    var toggles = document.getElementById("toggle-all-docs");
+    let toggles = document.getElementById("toggle-all-docs");
     if (toggles) {
         toggles.onclick = toggleAllDocs;
     }
@@ -2050,7 +2044,7 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function createSimpleToggle(sectionIsCollapsed) {
-        var toggle = document.createElement("a");
+        let toggle = document.createElement("a");
         toggle.href = "javascript:void(0)";
         toggle.className = "collapse-toggle";
         toggle.innerHTML = "[<span class=\"inner\">" + labelForToggleButton(sectionIsCollapsed) +
@@ -2058,10 +2052,10 @@ if (!DOMTokenList.prototype.remove) {
         return toggle;
     }
 
-    var toggle = createSimpleToggle(false);
+    let toggle = createSimpleToggle(false);
 
-    var func = function(e) {
-        var next = e.nextElementSibling;
+    let func = function(e) {
+        let next = e.nextElementSibling;
         if (!next) {
             return;
         }
@@ -2072,8 +2066,8 @@ if (!DOMTokenList.prototype.remove) {
         }
     };
 
-    var funcImpl = function(e) {
-        var next = e.nextElementSibling;
+    let funcImpl = function(e) {
+        let next = e.nextElementSibling;
         if (next && hasClass(next, "docblock")) {
             next = next.nextElementSibling;
         }
@@ -2088,7 +2082,7 @@ if (!DOMTokenList.prototype.remove) {
     onEachLazy(document.getElementsByClassName("method"), func);
     onEachLazy(document.getElementsByClassName("associatedconstant"), func);
     onEachLazy(document.getElementsByClassName("impl"), funcImpl);
-    var impl_call = function() {};
+    let impl_call = function() {};
     if (getCurrentValue("rustdoc-method-docs") !== "false") {
         impl_call = function(e, newToggle, pageId) {
             if (e.id.match(/^impl(?:-\d+)?$/) === null) {
@@ -2099,8 +2093,8 @@ if (!DOMTokenList.prototype.remove) {
             }
         };
     }
-    var pageId = getPageId();
-    var newToggle = document.createElement("a");
+    let pageId = getPageId();
+    let newToggle = document.createElement("a");
     newToggle.href = "javascript:void(0)";
     newToggle.className = "collapse-toggle hidden-default collapsed";
     newToggle.innerHTML = "[<span class=\"inner\">" + labelForToggleButton(true) +
@@ -2130,11 +2124,11 @@ if (!DOMTokenList.prototype.remove) {
     }
     onEachLazy(document.getElementsByClassName("impl-items"), function(e) {
         onEachLazy(e.getElementsByClassName("associatedconstant"), func);
-        var hiddenElems = e.getElementsByClassName("hidden");
-        var needToggle = false;
+        let hiddenElems = e.getElementsByClassName("hidden");
+        let needToggle = false;
 
-        var hlength = hiddenElems.length;
-        for (var i = 0; i < hlength; ++i) {
+        let hlength = hiddenElems.length;
+        for (let i = 0; i < hlength; ++i) {
             if (hasClass(hiddenElems[i], "content") === false &&
                 hasClass(hiddenElems[i], "docblock") === false) {
                 needToggle = true;
@@ -2142,7 +2136,7 @@ if (!DOMTokenList.prototype.remove) {
             }
         }
         if (needToggle === true) {
-            var inner_toggle = newToggle.cloneNode(true);
+            let inner_toggle = newToggle.cloneNode(true);
             inner_toggle.onclick = toggleClicked;
             e.insertBefore(inner_toggle, e.firstChild);
             impl_call(e, inner_toggle, pageId);
@@ -2150,7 +2144,7 @@ if (!DOMTokenList.prototype.remove) {
     });
 
     function createToggle(otherMessage, fontSize, extraClass, show) {
-        var span = document.createElement("span");
+        let span = document.createElement("span");
         span.className = "toggle-label";
         if (show) {
             span.style.display = "none";
@@ -2165,14 +2159,14 @@ if (!DOMTokenList.prototype.remove) {
             span.style.fontSize = fontSize;
         }
 
-        var mainToggle = toggle.cloneNode(true);
+        let mainToggle = toggle.cloneNode(true);
         mainToggle.appendChild(span);
 
-        var wrapper = document.createElement("div");
+        let wrapper = document.createElement("div");
         wrapper.className = "toggle-wrapper";
         if (!show) {
             addClass(wrapper, "collapsed");
-            var inner = mainToggle.getElementsByClassName("inner");
+            let inner = mainToggle.getElementsByClassName("inner");
             if (inner && inner.length > 0) {
                 inner[0].innerHTML = "+";
             }
@@ -2184,31 +2178,12 @@ if (!DOMTokenList.prototype.remove) {
         return wrapper;
     }
 
-    var showItemDeclarations = getCurrentValue("rustdoc-item-declarations") === "false";
+    let showItemDeclarations = getCurrentValue("rustdoc-item-declarations") === "false";
     function buildToggleWrapper(e) {
-        if (hasClass(e, "autohide")) {
-            var wrap = e.previousElementSibling;
-            if (wrap && hasClass(wrap, "toggle-wrapper")) {
-                var inner_toggle = wrap.childNodes[0];
-                var extra = e.childNodes[0].tagName === "H3";
-
-                e.style.display = "none";
-                addClass(wrap, "collapsed");
-                onEachLazy(inner_toggle.getElementsByClassName("inner"), function(e) {
-                    e.innerHTML = labelForToggleButton(true);
-                });
-                onEachLazy(inner_toggle.getElementsByClassName("toggle-label"), function(e) {
-                    e.style.display = "inline-block";
-                    if (extra === true) {
-                        i_e.innerHTML = " Show " + e.childNodes[0].innerHTML;
-                    }
-                });
-            }
-        }
         if (e.parentNode.id === "main") {
-            var otherMessage = "";
-            var fontSize;
-            var extraClass;
+            let otherMessage = "";
+            let fontSize;
+            let extraClass;
 
             if (hasClass(e, "type-decl")) {
                 fontSize = "20px";
@@ -2252,7 +2227,7 @@ if (!DOMTokenList.prototype.remove) {
         if (nb === 0 || nb === 1 || nb === 2) {
             currentTab = nb;
         }
-        var nb_copy = nb;
+        let nb_copy = nb;
         onEachLazy(document.getElementById("titles").childNodes, function(elem) {
             if (nb_copy === 0) {
                 addClass(elem, "selected");
@@ -2272,41 +2247,41 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function createToggleWrapper(tog) {
-        var span = document.createElement("span");
+        let span = document.createElement("span");
         span.className = "toggle-label";
         span.style.display = "none";
         span.innerHTML = "&nbsp;Expand&nbsp;attributes";
         tog.appendChild(span);
 
-        var wrapper = document.createElement("div");
+        let wrapper = document.createElement("div");
         wrapper.className = "toggle-wrapper toggle-attributes";
         wrapper.appendChild(tog);
         return wrapper;
     }
 
     // To avoid checking on "rustdoc-item-attributes" value on every loop...
-    var itemAttributesFunc = function() {};
+    let itemAttributesFunc = function() {};
     if (getCurrentValue("rustdoc-item-attributes") !== "false") {
         itemAttributesFunc = function(x) {
             collapseDocs(x.previousSibling.childNodes[0], "toggle");
         };
     }
-    var attributesToggle = createToggleWrapper(createSimpleToggle(false));
+    let attributesToggle = createToggleWrapper(createSimpleToggle(false));
     onEachLazy(main.getElementsByClassName("attributes"), function(i_e) {
         i_e.parentNode.insertBefore(attributesToggle.cloneNode(true), i_e);
         itemAttributesFunc(i_e);
     });
 
     // To avoid checking on "rustdoc-line-numbers" value on every loop...
-    var lineNumbersFunc = function() {};
+    let lineNumbersFunc = function() {};
     if (getCurrentValue("rustdoc-line-numbers") === "true") {
         lineNumbersFunc = function(x) {
-            var count = x.textContent.split("\n").length;
-            var elems = [];
-            for (var i = 0; i < count; ++i) {
+            let count = x.textContent.split("\n").length;
+            let elems = [];
+            for (let i = 0; i < count; ++i) {
                 elems.push(i + 1);
             }
-            var node = document.createElement("pre");
+            let node = document.createElement("pre");
             addClass(node, "line-number");
             node.innerHTML = elems.join("\n");
             x.parentNode.insertBefore(node, x);
@@ -2314,17 +2289,17 @@ if (!DOMTokenList.prototype.remove) {
     }
     onEachLazy(document.getElementsByClassName("rust-example-rendered"), function(e) {
         if (hasClass(e, "compile_fail")) {
-            e.addEventListener("mouseover", function(event) {
+            e.addEventListener("mouseover", function() {
                 this.parentElement.previousElementSibling.childNodes[0].style.color = "#f00";
             });
-            e.addEventListener("mouseout", function(event) {
+            e.addEventListener("mouseout", function() {
                 this.parentElement.previousElementSibling.childNodes[0].style.color = "";
             });
         } else if (hasClass(e, "ignore")) {
-            e.addEventListener("mouseover", function(event) {
+            e.addEventListener("mouseover", function() {
                 this.parentElement.previousElementSibling.childNodes[0].style.color = "#ff9200";
             });
-            e.addEventListener("mouseout", function(event) {
+            e.addEventListener("mouseout", function() {
                 this.parentElement.previousElementSibling.childNodes[0].style.color = "";
             });
         }
@@ -2332,7 +2307,7 @@ if (!DOMTokenList.prototype.remove) {
     });
 
     function showModal(content) {
-        var modal = document.createElement("div");
+        let modal = document.createElement("div");
         modal.id = "important";
         addClass(modal, "modal");
         modal.innerHTML = "<div class=\"modal-content\"><div class=\"close\" id=\"modal-close\">✕" +
@@ -2344,7 +2319,7 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function hideModal() {
-        var modal = document.getElementById("important");
+        let modal = document.getElementById("important");
         if (modal) {
             modal.parentNode.removeChild(modal);
         }
@@ -2374,18 +2349,18 @@ if (!DOMTokenList.prototype.remove) {
         };
     }
 
-    var params = getQueryStringParams();
+    let params = getQueryStringParams();
     if (params && params.search) {
         addClass(main, "hidden");
-        var search = document.getElementById("search");
+        let search = document.getElementById("search");
         removeClass(search, "hidden");
         search.innerHTML = "<h3 style=\"text-align: center;\">Loading search results...</h3>";
     }
 
-    var sidebar_menu = document.getElementsByClassName("sidebar-menu")[0];
+    let sidebar_menu = document.getElementsByClassName("sidebar-menu")[0];
     if (sidebar_menu) {
         sidebar_menu.onclick = function() {
-            var sidebar = document.getElementsByClassName("sidebar")[0];
+            let sidebar = document.getElementsByClassName("sidebar")[0];
             if (hasClass(sidebar, "mobile") === true) {
                 hideSidebar();
             } else {
@@ -2416,22 +2391,22 @@ if (!DOMTokenList.prototype.remove) {
     }
 
     function addSearchOptions(crates) {
-        var elem = document.getElementById('crate-search');
+        let elem = document.getElementById('crate-search');
 
         if (!elem) {
             return;
         }
-        var crates_text = [];
+        let crates_text = [];
         if (crates.length > 1) {
-            for (var crate in crates) {
+            for (let crate in crates) {
                 if (crates.hasOwnProperty(crate)) {
                     crates_text.push(crate);
                 }
             }
         }
         crates_text.sort(function(a, b) {
-            var lower_a = a.toLowerCase();
-            var lower_b = b.toLowerCase();
+            let lower_a = a.toLowerCase();
+            let lower_b = b.toLowerCase();
 
             if (lower_a < lower_b) {
                 return -1;
@@ -2440,8 +2415,8 @@ if (!DOMTokenList.prototype.remove) {
             }
             return 0;
         });
-        for (var i = 0; i < crates_text.length; ++i) {
-            var option = document.createElement("option");
+        for (let i = 0; i < crates_text.length; ++i) {
+            let option = document.createElement("option");
             option.value = crates_text[i];
             option.innerText = crates_text[i];
             elem.appendChild(option);
diff --git a/src/librustdoc/html/static/settings.js b/src/librustdoc/html/static/settings.js
index c21db7371f3c3..e985c4f8ba24a 100644
--- a/src/librustdoc/html/static/settings.js
+++ b/src/librustdoc/html/static/settings.js
@@ -1,3 +1,6 @@
+// Local js definitions:
+/* global getCurrentValue, updateLocalStorage */
+
 (function () {
     function changeSetting(settingName, isEnabled) {
         updateLocalStorage('rustdoc-' + settingName, isEnabled);
@@ -8,14 +11,14 @@
     }
 
     function setEvents() {
-        var elems = document.getElementsByClassName("slider");
+        let elems = document.getElementsByClassName("slider");
         if (!elems || elems.length === 0) {
             return;
         }
-        for (var i = 0; i < elems.length; ++i) {
-            var toggle = elems[i].previousElementSibling;
-            var settingId = toggle.id;
-            var settingValue = getSettingValue(settingId);
+        for (let i = 0; i < elems.length; ++i) {
+            let toggle = elems[i].previousElementSibling;
+            let settingId = toggle.id;
+            let settingValue = getSettingValue(settingId);
             if (settingValue !== null) {
                 toggle.checked = settingValue === "true";
             }
diff --git a/src/librustdoc/html/static/source-script.js b/src/librustdoc/html/static/source-script.js
index 0affe1c6812f5..2780cadb7a6d8 100644
--- a/src/librustdoc/html/static/source-script.js
+++ b/src/librustdoc/html/static/source-script.js
@@ -1,19 +1,22 @@
 // From rust:
 /* global sourcesIndex */
 
+// From DOM global ids:
+/* global search */
+
 // Local js definitions:
 /* global addClass, getCurrentValue, hasClass, removeClass, updateLocalStorage */
 
 function getCurrentFilePath() {
-    var parts = window.location.pathname.split("/");
-    var rootPathParts = window.rootPath.split("/");
+    let parts = window.location.pathname.split("/");
+    let rootPathParts = window.rootPath.split("/");
 
-    for (var i = 0; i < rootPathParts.length; ++i) {
+    for (let i = 0; i < rootPathParts.length; ++i) {
         if (rootPathParts[i] === "..") {
             parts.pop();
         }
     }
-    var file = window.location.pathname.substring(parts.join("/").length);
+    let file = window.location.pathname.substring(parts.join("/").length);
     if (file.startsWith("/")) {
         file = file.substring(1);
     }
@@ -21,7 +24,7 @@ function getCurrentFilePath() {
 }
 
 function createDirEntry(elem, parent, fullPath, currentFile, hasFoundFile) {
-    var name = document.createElement("div");
+    let name = document.createElement("div");
     name.className = "name";
 
     fullPath += elem["name"] + "/";
@@ -35,11 +38,11 @@ function createDirEntry(elem, parent, fullPath, currentFile, hasFoundFile) {
     };
     name.innerText = elem["name"];
 
-    var children = document.createElement("div");
+    let children = document.createElement("div");
     children.className = "children";
-    var folders = document.createElement("div");
+    let folders = document.createElement("div");
     folders.className = "folders";
-    for (var i = 0; i < elem.dirs.length; ++i) {
+    for (let i = 0; i < elem.dirs.length; ++i) {
         if (createDirEntry(elem.dirs[i], folders, fullPath, currentFile,
                            hasFoundFile) === true) {
             addClass(name, "expand");
@@ -48,10 +51,10 @@ function createDirEntry(elem, parent, fullPath, currentFile, hasFoundFile) {
     }
     children.appendChild(folders);
 
-    var files = document.createElement("div");
+    let files = document.createElement("div");
     files.className = "files";
-    for (i = 0; i < elem.files.length; ++i) {
-        var file = document.createElement("a");
+    for (let i = 0; i < elem.files.length; ++i) {
+        let file = document.createElement("a");
         file.innerText = elem.files[i];
         file.href = window.rootPath + "src/" + fullPath + elem.files[i] + ".html";
         if (hasFoundFile === false &&
@@ -70,8 +73,8 @@ function createDirEntry(elem, parent, fullPath, currentFile, hasFoundFile) {
 }
 
 function toggleSidebar() {
-    var sidebar = document.getElementById("source-sidebar");
-    var child = this.children[0].children[0];
+    let sidebar = document.getElementById("source-sidebar");
+    let child = this.children[0].children[0];
     if (child.innerText === ">") {
         sidebar.style.left = "";
         this.style.left = "";
@@ -86,14 +89,14 @@ function toggleSidebar() {
 }
 
 function createSidebarToggle() {
-    var sidebarToggle = document.createElement("div");
+    let sidebarToggle = document.createElement("div");
     sidebarToggle.id = "sidebar-toggle";
     sidebarToggle.onclick = toggleSidebar;
 
-    var inner1 = document.createElement("div");
+    let inner1 = document.createElement("div");
     inner1.style.position = "relative";
 
-    var inner2 = document.createElement("div");
+    let inner2 = document.createElement("div");
     inner2.style.marginTop = "-2px";
     if (getCurrentValue("rustdoc-source-sidebar-show") === "true") {
         inner2.innerText = "<";
@@ -111,21 +114,21 @@ function createSourceSidebar() {
     if (window.rootPath.endsWith("/") === false) {
         window.rootPath += "/";
     }
-    var main = document.getElementById("main");
+    let main = document.getElementById("main");
 
-    var sidebarToggle = createSidebarToggle();
+    let sidebarToggle = createSidebarToggle();
     main.insertBefore(sidebarToggle, main.firstChild);
 
-    var sidebar = document.createElement("div");
+    let sidebar = document.createElement("div");
     sidebar.id = "source-sidebar";
     if (getCurrentValue("rustdoc-source-sidebar-show") !== "true") {
         sidebar.style.left = "-300px";
     }
 
-    var currentFile = getCurrentFilePath();
-    var hasFoundFile = false;
+    let currentFile = getCurrentFilePath();
+    let hasFoundFile = false;
 
-    var title = document.createElement("div");
+    let title = document.createElement("div");
     title.className = "title";
     title.innerText = "Files";
     sidebar.appendChild(title);
diff --git a/src/librustdoc/html/static/storage.js b/src/librustdoc/html/static/storage.js
index d5dea247d28d1..00741619d2dd7 100644
--- a/src/librustdoc/html/static/storage.js
+++ b/src/librustdoc/html/static/storage.js
@@ -1,6 +1,9 @@
 // From rust:
 /* global resourcesSuffix */
 
+// eslint doesn't understand the functions here are used elsewhere
+/* eslint no-unused-vars: "off" */
+
 var currentTheme = document.getElementById("themeStyle");
 var mainTheme = document.getElementById("mainThemeStyle");
 
@@ -30,15 +33,15 @@ function isHidden(elem) {
 
 function onEach(arr, func, reversed) {
     if (arr && arr.length > 0 && func) {
-        var length = arr.length;
+        let length = arr.length;
         if (reversed !== true) {
-            for (var i = 0; i < length; ++i) {
+            for (let i = 0; i < length; ++i) {
                 if (func(arr[i]) === true) {
                     return true;
                 }
             }
         } else {
-            for (var i = length - 1; i >= 0; --i) {
+            for (let i = length - 1; i >= 0; --i) {
                 if (func(arr[i]) === true) {
                     return true;
                 }
@@ -89,15 +92,15 @@ function getCurrentValue(name) {
 }
 
 function switchTheme(styleElem, mainStyleElem, newTheme) {
-    var fullBasicCss = "rustdoc" + resourcesSuffix + ".css";
-    var fullNewTheme = newTheme + resourcesSuffix + ".css";
-    var newHref = mainStyleElem.href.replace(fullBasicCss, fullNewTheme);
+    let fullBasicCss = "rustdoc" + resourcesSuffix + ".css";
+    let fullNewTheme = newTheme + resourcesSuffix + ".css";
+    let newHref = mainStyleElem.href.replace(fullBasicCss, fullNewTheme);
 
     if (styleElem.href === newHref) {
         return;
     }
 
-    var found = false;
+    let found = false;
     if (savedHref.length === 0) {
         onEachLazy(document.getElementsByTagName("link"), function(el) {
             savedHref.push(el.href);
diff --git a/src/tools/rustdoc-js/tester.js b/src/tools/rustdoc-js/tester.js
index c41da93a98310..7150241ee4dba 100644
--- a/src/tools/rustdoc-js/tester.js
+++ b/src/tools/rustdoc-js/tester.js
@@ -81,9 +81,9 @@ function extractFunction(content, functionName) {
 
 // Stupid function extractor for array.
 function extractArrayVariable(content, arrayName) {
-    var splitter = "var " + arrayName;
+    var splitter = new RegExp("(?:var|const|let) " + arrayName);
     while (true) {
-        var start = content.indexOf(splitter);
+        var start = content.search(splitter);
         if (start === -1) {
             break;
         }
@@ -126,9 +126,9 @@ function extractArrayVariable(content, arrayName) {
 
 // Stupid function extractor for variable.
 function extractVariable(content, varName) {
-    var splitter = "var " + varName;
+    var splitter = new RegExp("(?:var|const|let) " + varName);
     while (true) {
-        var start = content.indexOf(splitter);
+        var start = content.search(splitter);
         if (start === -1) {
             break;
         }