1 files changed, 70 insertions, 0 deletions
diff --git a/js/mixins/dom_iterable.ts b/js/mixins/dom_iterable.ts
new file mode 100644
index 000000000..015226589
--- /dev/null
+++ b/js/mixins/dom_iterable.ts
@@ -0,0 +1,70 @@
+import { DomIterable } from "../dom_types";
+import { globalEval } from "../global_eval";
+
+// if we import it directly from "globals" it will break the unit tests so we
+// have to grab a reference to the global scope a different way
+const window = globalEval("this");
+
+// tslint:disable:no-any
+type Constructor<T = {}> = new (...args: any[]) => T;
+
+/** Mixes in a DOM iterable methods into a base class, assumes that there is
+ * a private data iterable that is part of the base class, located at
+ * `[dataSymbol]`.
+ */
+export function DomIterableMixin<K, V, TBase extends Constructor>(
+  // tslint:disable-next-line:variable-name
+  Base: TBase,
+  dataSymbol: symbol
+): TBase & Constructor<DomIterable<K, V>> {
+  // we have to cast `this` as `any` because there is no way to describe the
+  // Base class in a way where the Symbol `dataSymbol` is defined.  So the
+  // runtime code works, but we do lose a little bit of type safety.
+
+  // tslint:disable-next-line:variable-name
+  const DomIterable = class extends Base {
+    *entries(): IterableIterator<[K, V]> {
+      for (const entry of (this as any)[dataSymbol].entries()) {
+        yield entry;
+      }
+    }
+
+    *keys(): IterableIterator<K> {
+      for (const key of (this as any)[dataSymbol].keys()) {
+        yield key;
+      }
+    }
+
+    *values(): IterableIterator<V> {
+      for (const value of (this as any)[dataSymbol].values()) {
+        yield value;
+      }
+    }
+
+    forEach(
+      callbackfn: (value: V, key: K, parent: this) => void,
+      // tslint:disable-next-line:no-any
+      thisArg?: any
+    ): void {
+      callbackfn = callbackfn.bind(thisArg == null ? window : Object(thisArg));
+      for (const [key, value] of (this as any)[dataSymbol].entries()) {
+        callbackfn(value, key, this);
+      }
+    }
+
+    *[Symbol.iterator](): IterableIterator<[K, V]> {
+      for (const entry of (this as any)[dataSymbol]) {
+        yield entry;
+      }
+    }
+  };
+
+  // we want the Base class name to be the name of the class.
+  Object.defineProperty(DomIterable, "name", {
+    value: Base.name,
+    configurable: true
+  });
+
+  return DomIterable;
+}
+// tslint:enable:no-any