1 files changed, 26 insertions, 0 deletions
diff --git a/std/async/deferred.ts b/std/async/deferred.ts
new file mode 100644
index 000000000..109a1a37e
--- /dev/null
+++ b/std/async/deferred.ts
@@ -0,0 +1,26 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+// TODO(ry) It'd be better to make Deferred 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 Deferred<T> extends Promise<T> {
+  resolve: (value?: T | PromiseLike<T>) => void;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  reject: (reason?: any) => void;
+}
+
+/** Creates a Promise with the `reject` and `resolve` functions
+ * placed as methods on the promise object itself. It allows you to do:
+ *
+ *     const p = deferred<number>();
+ *     // ...
+ *     p.resolve(42);
+ */
+export function deferred<T>(): Deferred<T> {
+  let methods;
+  const promise = new Promise<T>((resolve, reject): void => {
+    methods = { resolve, reject };
+  });
+  return Object.assign(promise, methods) as Deferred<T>;
+}