diff --git a/samples/excel/44-shape/shape-images.yaml b/samples/excel/44-shape/shape-images.yaml
index a955ab46..b70079c4 100644
--- a/samples/excel/44-shape/shape-images.yaml
+++ b/samples/excel/44-shape/shape-images.yaml
@@ -19,8 +19,8 @@ script:
 
             reader.onload = (event) => {
                 Excel.run((context) => {
-                    const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-                    const mybase64 = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+                    const startIndex = reader.result.toString().indexOf("base64,");
+                    const mybase64 = reader.result.toString().substr(startIndex + 7);
                     const sheet = context.workbook.worksheets.getItem("Shapes");
                     const image = sheet.shapes.addImage(mybase64);
                     image.name = "Image";
diff --git a/samples/excel/50-workbook/create-workbook.yaml b/samples/excel/50-workbook/create-workbook.yaml
index 34b85bca..e5b1ea75 100644
--- a/samples/excel/50-workbook/create-workbook.yaml
+++ b/samples/excel/50-workbook/create-workbook.yaml
@@ -24,8 +24,8 @@ script:
             reader.onload = ((event) => {
                 Excel.run(context => {
                     // strip off the metadata before the base64-encoded string
-                    const startIndex = (<FileReader>event.target).result.indexOf("base64,");
-                    const mybase64 = (<FileReader>event.target).result.substr(startIndex + 7);
+                    const startIndex = reader.result.toString().indexOf("base64,");
+                    const mybase64 = reader.result.toString().substr(startIndex + 7);
 
                     Excel.createWorkbook(mybase64);
                     return context.sync();
diff --git a/samples/excel/85-preview-apis/workbook-insert-external-worksheets.yaml b/samples/excel/85-preview-apis/workbook-insert-external-worksheets.yaml
index 375e8dd6..2ae010e8 100644
--- a/samples/excel/85-preview-apis/workbook-insert-external-worksheets.yaml
+++ b/samples/excel/85-preview-apis/workbook-insert-external-worksheets.yaml
@@ -16,8 +16,8 @@ script:
             reader.onload = (event) => {
                 Excel.run((context) => {
                     // strip off the metadata before the base64-encoded string
-                    const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-                    const workbookContents = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+                    const startIndex = reader.result.toString().indexOf("base64,");
+                    const workbookContents = reader.result.toString().substr(startIndex + 7);
 
                     const sheets = context.workbook.worksheets;
                     sheets.addFromBase64(
diff --git a/samples/excel/99-just-for-fun/tetrominos.yaml b/samples/excel/99-just-for-fun/tetrominos.yaml
index 06ce38b9..19ee7a37 100644
--- a/samples/excel/99-just-for-fun/tetrominos.yaml
+++ b/samples/excel/99-just-for-fun/tetrominos.yaml
@@ -23,8 +23,8 @@ script:
             const reader = new FileReader();
 
             reader.onload = (event) => {
-                const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-                const mybase64 = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+                const startIndex = reader.result.toString().indexOf("base64,");
+                const mybase64 = reader.result.toString().substr(startIndex + 7);
                 backgroundPicture = mybase64;
             };
 
diff --git a/samples/powerpoint/basics/create-presentation.yaml b/samples/powerpoint/basics/create-presentation.yaml
index 7113cca3..990e8bef 100644
--- a/samples/powerpoint/basics/create-presentation.yaml
+++ b/samples/powerpoint/basics/create-presentation.yaml
@@ -21,8 +21,8 @@ script:
 
             reader.onload = (event) => {
                 // strip off the metadata before the base64-encoded string
-                const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-                const copyBase64 = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+                const startIndex = reader.result.toString().indexOf("base64,");
+                const copyBase64 = reader.result.toString().substr(startIndex + 7);
 
                 PowerPoint.createPresentation(copyBase64);        
             };
diff --git a/snippet-extractor-output/snippets.yaml b/snippet-extractor-output/snippets.yaml
index 2c9a2123..06fc8fd0 100644
--- a/snippet-extractor-output/snippets.yaml
+++ b/snippet-extractor-output/snippets.yaml
@@ -2699,8 +2699,8 @@ Excel.ShapeCollection.addImage:
 
     reader.onload = (event) => {
         Excel.run((context) => {
-            const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-            const mybase64 = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+            const startIndex = reader.result.toString().indexOf("base64,");
+            const mybase64 = reader.result.toString().substr(startIndex + 7);
             const sheet = context.workbook.worksheets.getItem("Shapes");
             const image = sheet.shapes.addImage(mybase64);
             image.name = "Image";
@@ -3276,8 +3276,8 @@ Excel.WorksheetCollection.addFromBase64:
     reader.onload = (event) => {
         Excel.run((context) => {
             // strip off the metadata before the base64-encoded string
-            const startIndex = (<string>(<FileReader>event.target).result).indexOf("base64,");
-            const workbookContents = (<string>(<FileReader>event.target).result).substr(startIndex + 7);
+            const startIndex = reader.result.toString().indexOf("base64,");
+            const workbookContents = reader.result.toString().substr(startIndex + 7);
 
             const sheets = context.workbook.worksheets;
             sheets.addFromBase64(