1 files changed, 25 insertions, 0 deletions
diff --git a/util.ts b/util.ts
index c4fa03255..67d3b550e 100644
--- a/util.ts
+++ b/util.ts
@@ -20,3 +20,28 @@ export function typedArrayToArrayBuffer(ta: TypedArray): ArrayBuffer {
   const ab = ta.buffer.slice(ta.byteOffset, ta.byteOffset + ta.byteLength);
   return ab as ArrayBuffer;
 }
+
+// A `Resolvable` is a Promise with the `reject` and `resolve` functions
+// placed as methods on the promise object itself. It allows you to do:
+//
+//   const p = createResolvable<number>();
+//   ...
+//   p.resolve(42);
+//
+// It'd be prettier to make Resolvable a class that inherits from Promise,
+// rather than an interface. This is possible in ES2016, however typescript
+// produces broken code when targeting ES5 code.
+// See https://github.com/Microsoft/TypeScript/issues/15202
+// At the time of writing, the github issue is closed but the problem remains.
+export interface Resolvable<T> extends Promise<T> {
+  resolve: (value?: T | PromiseLike<T>) => void;
+  // tslint:disable-next-line:no-any
+  reject: (reason?: any) => void;
+}
+export function createResolvable<T>(): Resolvable<T> {
+  let methods;
+  const promise = new Promise<T>((resolve, reject) => {
+    methods = { resolve, reject };
+  });
+  return Object.assign(promise, methods) as Resolvable<T>;
+}