V8 Microtask Queue & API

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index c1955cfdf7b71eb41e11af3e312992e0305922f1..3f993a2444951de9791b0008c1177ffd5971177a 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -1906,7 +1906,16 @@ function RunMicrotasks() {
     RunMicrotasks.queue = new InternalArray;
 
     for (var i = 0; i < microtasks.length; i++) {
-      microtasks[i]();
+      var microtask = microtasks[i];
+      if (typeof microtask === 'function')
+        microtask();
+      else
+        %RunExternalMicrotask(microtask);
     }
   }
 }
+
+function EnqueueExternalMicrotask(handler) {
+  %SetMicrotaskPending(true);
+  RunMicrotasks.queue.push(handler);
+}