5 files changed, 49 insertions, 0 deletions
diff --git a/core/libdeno/binding.cc b/core/libdeno/binding.cc
index 291e62f01..7827cd522 100644
--- a/core/libdeno/binding.cc
+++ b/core/libdeno/binding.cc
@@ -455,6 +455,16 @@ void EvalContext(const v8::FunctionCallbackInfo<v8::Value>& args) {
   args.GetReturnValue().Set(output);
 }
 
+void QueueMicrotask(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  v8::Isolate* isolate = args.GetIsolate();
+
+  if (!(args[0]->IsFunction())) {
+    ThrowInvalidArgument(isolate);
+    return;
+  }
+  isolate->EnqueueMicrotask(args[0].As<v8::Function>());
+}
+
 void InitializeContext(v8::Isolate* isolate, v8::Local<v8::Context> context) {
   v8::HandleScope handle_scope(isolate);
   v8::Context::Scope context_scope(context);
@@ -493,6 +503,15 @@ void InitializeContext(v8::Isolate* isolate, v8::Local<v8::Context> context) {
 
   CHECK(core_val->SetAccessor(context, deno::v8_str("shared"), Shared)
             .FromJust());
+
+  // Direct bindings on `window`.
+  auto queue_microtask_tmpl =
+      v8::FunctionTemplate::New(isolate, QueueMicrotask);
+  auto queue_microtask_val =
+      queue_microtask_tmpl->GetFunction(context).ToLocalChecked();
+  CHECK(
+      global->Set(context, deno::v8_str("queueMicrotask"), queue_microtask_val)
+          .FromJust());
 }
 
 void MessageCallback(v8::Local<v8::Message> message,
diff --git a/core/libdeno/internal.h b/core/libdeno/internal.h
index 50e85017e..f3789fcc3 100644
--- a/core/libdeno/internal.h
+++ b/core/libdeno/internal.h
@@ -156,6 +156,7 @@ void ErrorToJSON(const v8::FunctionCallbackInfo<v8::Value>& args);
 void Shared(v8::Local<v8::Name> property,
             const v8::PropertyCallbackInfo<v8::Value>& info);
 void MessageCallback(v8::Local<v8::Message> message, v8::Local<v8::Value> data);
+void QueueMicrotask(const v8::FunctionCallbackInfo<v8::Value>& args);
 static intptr_t external_references[] = {
     reinterpret_cast<intptr_t>(Print),
     reinterpret_cast<intptr_t>(Recv),
@@ -164,6 +165,7 @@ static intptr_t external_references[] = {
     reinterpret_cast<intptr_t>(ErrorToJSON),
     reinterpret_cast<intptr_t>(Shared),
     reinterpret_cast<intptr_t>(MessageCallback),
+    reinterpret_cast<intptr_t>(QueueMicrotask),
     0};
 
 static const deno_buf empty_buf = {nullptr, 0};
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;
 }