Iterator polyfill

src/util/iterator/polyfill.ts

@@ -4,10 +4,167 @@ if (typeof Iterator === 'undefined' && typeof globalThis === 'object') {
       return this;
     }
 
-    public find(predicate: (value: unknown) => boolean): T | undefined {
-      for (const value of this as any) if (predicate(value)) return value;
+    /**
+     * Returns the value of the first element in this iterator where predicate
+     * is true, and `undefined` otherwise.
+     *
+     * @param predicate find calls predicate once for each element of this iterator, in
+     *     order, until it finds one where predicate returns true. If such an element is found, find
+     *     immediately returns that element value. Otherwise, find returns undefined.
+     */
+    find<S extends T>(predicate: (value: T, index: number) => value is S): S | undefined;
+    find(predicate: (value: T, index: number) => unknown): T | undefined {
+      let index = 0;
+      for (const value of this as any) if (predicate(value, index++)) return value;
       return;
     }
+
+    /**
+     * Creates an iterator whose values are the result of applying the callback
+     * to the values from this iterator.
+     *
+     * @param callbackfn A function that accepts up to two arguments to be used
+     *     to transform values from the underlying iterator.
+     */
+    *map<U>(callbackfn: (value: T, index: number) => U): IteratorObject<U, undefined, unknown> {
+      let index = 0;
+      for (const value of this as any) yield callbackfn(value, index++);
+    }
+
+    /**
+     * Creates an iterator whose values are those from this iterator for which
+     * the provided predicate returns true.
+     *
+     * @param predicate A function that accepts up to two arguments to be used
+     *     to test values from the underlying iterator.
+     */
+    filter<S extends T>(predicate: (value: T, index: number) => value is S): IteratorObject<S, undefined, unknown>
+    *filter(predicate: (value: T, index: number) => unknown): IteratorObject<T, undefined, unknown> {
+      let index = 0;
+      for (const value of this as any) if (predicate(value, index++)) yield value;
+    }
+
+    /**
+     * Creates an iterator whose values are the values from this iterator,
+     * stopping once the provided limit is reached.
+     *
+     * @param limit The maximum number of values to yield.
+     */
+    *take(limit: number): IteratorObject<T, undefined, unknown> {
+      let index = 0;
+      for (const value of this as any) {
+        if (index++ >= limit) break;
+        yield value;
+      }
+    }
+
+    /**
+     * Creates an iterator whose values are the values from this iterator after
+     * skipping the provided count.
+     *
+     * @param count The number of values to drop.
+     */
+    *drop(count: number): IteratorObject<T, undefined, unknown> {
+      let index = 0;
+      for (const value of this as any) {
+        if (index++ < count) continue;
+        yield value;
+      }
+    }
+
+    /**
+     * Creates an iterator whose values are the result of applying the callback
+     * to the values from this iterator and then flattening the resulting
+     * iterators or iterables.
+     *
+     * @param callback A function that accepts up to two arguments to be used
+     * to transform values from the underlying iterator into new iterators or
+     * iterables to be flattened into the result.
+     */
+    *flatMap<U>(callback: (value: T, index: number) => Iterator<U> | Iterable<U, unknown, undefined>): IteratorObject<U, undefined, unknown> {
+      let index = 0;
+      for (const value of this as any) {
+        const result = callback(value, index++);
+        if (result instanceof Iterator) {
+          for (const item of result as any) yield item;
+        } else {
+          for (const item of result as Iterable<U, unknown, undefined>) yield item;
+        }
+      }
+    }
+
+    /**
+     * Calls the specified callback function for all the elements in this
+     * iterator. The return value of the callback function is the accumulated
+     * result, and is provided as an argument in the next call to the callback
+     * function.
+     *
+     * @param callbackfn A function that accepts up to three arguments.
+     *     The reduce method calls the callbackfn function one time for each
+     *     element in the iterator.
+     * @param initialValue If initialValue is specified, it is used as the
+     *     initial value to start the accumulation. The first call to the
+     *     callbackfn function provides this value as an argument instead of a
+     *     value from the iterator.
+     */
+    reduce(callbackfn: (previousValue: T, currentValue: T, currentIndex: number) => T): T;
+    reduce(callbackfn: (previousValue: T, currentValue: T, currentIndex: number) => T, initialValue: T): T;
+    reduce<U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number) => U, initialValue: U): U;
+    reduce<U>(callbackfn: (previousValue: T | U, currentValue: T, currentIndex: number) => T | U, initialValue?: T | U): any {
+      let index = 0;
+      let accumulator: T | U = initialValue as any;
+      for (const value of this as any)
+        accumulator = callbackfn(accumulator, value, index++);
+      return accumulator;
+    }
+
+    /**
+     * Creates a new array from the values yielded by this iterator.
+     */
+    toArray(): T[] {
+      return [...this as any];
+    }
+
+    /**
+     * Performs the specified action for each element in the iterator.
+     * @param callbackfn A function that accepts up to two arguments. forEach calls the callbackfn function one time for each element in the iterator.
+     */
+    forEach(callbackfn: (value: T, index: number) => void): void {
+      let index = 0;
+      for (const value of this as any) callbackfn(value, index++);
+    }
+
+    /**
+     * Determines whether the specified callback function returns true for
+     * any element of this iterator.
+     *
+     * @param predicate A function that accepts up to two arguments. The some
+     *     method calls the predicate function for each element in this
+     *     iterator until the predicate returns a value true, or until the end
+     *     of the iterator.
+     */
+    some(predicate: (value: T, index: number) => unknown): boolean {
+      let index = 0;
+      for (const value of this as any)
+        if (predicate(value, index++)) return true;
+      return false;
+    }
+
+    /**
+     * Determines whether all the members of this iterator satisfy the
+     * specified test.
+     *
+     * @param predicate A function that accepts up to two arguments. The every
+     *     method calls the predicate function for each element in this
+     *     iterator until the predicate returns false, or until the end of
+     *     this iterator.
+     */
+    every(predicate: (value: T, index: number) => unknown): boolean {
+      let index = 0;
+      for (const value of this as any)
+        if (!predicate(value, index++)) return false;
+      return true;
+    }
   }
 
   /**