2 files changed, 58 insertions, 0 deletions
diff --git a/util/deferred.ts b/util/deferred.ts
new file mode 100644
index 000000000..f52087547
--- /dev/null
+++ b/util/deferred.ts
@@ -0,0 +1,42 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+export type Deferred<T = any, R = Error> = {
+  promise: Promise<T>;
+  resolve: (t?: T) => void;
+  reject: (r?: R) => void;
+  readonly handled: boolean;
+};
+
+/** Create deferred promise that can be resolved and rejected by outside */
+export function defer<T>(): Deferred<T> {
+  let handled = false;
+  let resolve;
+  let reject;
+  const promise = new Promise<T>((res, rej) => {
+    resolve = r => {
+      handled = true;
+      res(r);
+    };
+    reject = r => {
+      handled = true;
+      rej(r);
+    };
+  });
+  return {
+    promise,
+    resolve,
+    reject,
+    get handled() {
+      return handled;
+    }
+  };
+}
+
+export function isDeferred(x): x is Deferred {
+  return (
+    typeof x === "object" &&
+    x.promise instanceof Promise &&
+    typeof x["resolve"] === "function" &&
+    typeof x["reject"] === "function"
+  );
+}
diff --git a/util/deferred_test.ts b/util/deferred_test.ts
new file mode 100644
index 000000000..a397b3012
--- /dev/null
+++ b/util/deferred_test.ts
@@ -0,0 +1,16 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+import { assert, test } from "../testing/mod.ts";
+import { defer, isDeferred } from "./deferred.ts";
+
+test(async function asyncIsDeferred() {
+  const d = defer();
+  assert.assert(isDeferred(d));
+  assert.assert(
+    isDeferred({
+      promise: null,
+      resolve: () => {},
+      reject: () => {}
+    }) === false
+  );
+});