feat(util): 🎸 add basic Iterator polyfill

Author: streamich

src/util/iterator.ts renamed to src/util/iterator/index.ts

@@ -1,9 +1,9 @@
+import './polyfill';
+
 /**
  * Next function which returns `undefined` or a value of type `T`.
  * This is used in iterators that can end with an `undefined` value, which
  * indicates the end of iteration.
- *
- * @todo Rename to `UndEndNext`.
  */
 export type UndEndNext<T> = () => undefined | T;
 

src/util/iterator/polyfill.ts

@@ -0,0 +1,17 @@
+if (typeof Iterator === 'undefined' && typeof globalThis === 'object') {
+  class Iterator<T> {
+    [Symbol.iterator]() {
+      return this;
+    }
+
+    public find(predicate: (value: unknown) => boolean): T | undefined {
+      for (const value of this as any) if (predicate(value)) return value;
+      return;
+    }
+  }
+
+  /**
+   * The `Iterator` global class is new, so we need to check if it exists.
+   */
+  (globalThis as any).Iterator = Iterator;
+}