Add window.queueMicrotask (#2844)

3 files changed, 28 insertions, 0 deletions

diff --git a/js/globals.ts b/js/globals.ts
index b47cd80f3..ed7621165 100644
--- a/js/globals.ts
+++ b/js/globals.ts
@@ -89,6 +89,7 @@ window.onload = undefined as undefined | Function;
 // standard https://www.w3.org/TR/WebCryptoAPI/#crypto-interface as it does not
 // yet incorporate the SubtleCrypto interface as its "subtle" property.
 window.crypto = (csprng as unknown) as Crypto;
+// window.queueMicrotask added by hand to self-maintained lib.deno_runtime.d.ts
 
 // When creating the runtime type library, we use modifications to `window` to
 // determine what is in the global namespace.  When we put a class in the
diff --git a/js/globals_test.ts b/js/globals_test.ts
index 3085118de..42a055087 100644
--- a/js/globals_test.ts
+++ b/js/globals_test.ts
@@ -77,3 +77,29 @@ test(function DenoNamespaceImmutable(): void {
   // @ts-ignore
   assert(print === Deno.core.print);
 });
+
+test(async function windowQueueMicrotask(): Promise<void> {
+  let resolve1: () => void | undefined;
+  let resolve2: () => void | undefined;
+  let microtaskDone = false;
+  const p1 = new Promise(
+    (res): void => {
+      resolve1 = (): void => {
+        microtaskDone = true;
+        res();
+      };
+    }
+  );
+  const p2 = new Promise(
+    (res): void => {
+      resolve2 = (): void => {
+        assert(microtaskDone);
+        res();
+      };
+    }
+  );
+  window.queueMicrotask(resolve1!);
+  setTimeout(resolve2!, 0);
+  await p1;
+  await p2;
+});
diff --git a/js/lib.deno_runtime.d.ts b/js/lib.deno_runtime.d.ts
index bbdc1fcb9..8ece99581 100644
--- a/js/lib.deno_runtime.d.ts
+++ b/js/lib.deno_runtime.d.ts
@@ -1264,6 +1264,7 @@ declare interface Window {
     callback: (event: domTypes.Event) => void | null,
     options?: boolean | domTypes.EventListenerOptions | undefined
   ) => void;
+  queueMicrotask: (task: () => void) => void;
   Deno: typeof Deno;
 }