feat: queueMicrotask support (NativeScript#291)

Author: NathanWalker

NativeScript/runtime/Runtime.mm

@@ -193,6 +193,21 @@ void DisposeIsolateWhenPossible(Isolate* isolate) {
   DefinePerformanceObject(isolate, globalTemplate);
   DefineTimeMethod(isolate, globalTemplate);
   DefineDrainMicrotaskMethod(isolate, globalTemplate);
+  // queueMicrotask(callback) per spec
+  {
+    Local<FunctionTemplate> qmtTemplate = FunctionTemplate::New(
+        isolate, [](const FunctionCallbackInfo<Value>& info) {
+          auto* isolate = info.GetIsolate();
+          if (info.Length() < 1 || !info[0]->IsFunction()) {
+            isolate->ThrowException(Exception::TypeError(
+                tns::ToV8String(isolate, "queueMicrotask: callback must be a function")));
+            return;
+          }
+          v8::Local<v8::Function> cb = info[0].As<v8::Function>();
+          isolate->EnqueueMicrotask(cb);
+        });
+    globalTemplate->Set(tns::ToV8String(isolate, "queueMicrotask"), qmtTemplate);
+  }
   ObjectManager::Init(isolate, globalTemplate);
   //    SetTimeout::Init(isolate, globalTemplate);
   MetadataBuilder::RegisterConstantsOnGlobalObject(isolate, globalTemplate, isWorker);

TestRunner/app/tests/RuntimeImplementedAPIs.js

@@ -44,3 +44,37 @@ describe("Performance object", () => {
     expect(Math.abs(dateNow - performanceAccurateNow)).toBeLessThan(10);
   });
 });
+
+describe("queueMicrotask", () => {
+  it("should be defined as a function", () => {
+    expect(typeof queueMicrotask).toBe("function");
+  });
+
+  it("should throw TypeError when callback is not a function", () => {
+    expect(() => queueMicrotask(null)).toThrow();
+    expect(() => queueMicrotask(42)).toThrow();
+    expect(() => queueMicrotask({})).toThrow();
+  });
+
+  it("runs after current stack but before setTimeout(0)", (done) => {
+    const order = [];
+    queueMicrotask(() => order.push("microtask"));
+    setTimeout(() => {
+      order.push("timeout");
+      expect(order).toEqual(["microtask", "timeout"]);
+      done();
+    }, 0);
+    expect(order.length).toBe(0);
+  });
+
+  it("preserves ordering with Promise microtasks", (done) => {
+    const order = [];
+    queueMicrotask(() => order.push("qm1"));
+    Promise.resolve().then(() => order.push("p"));
+    queueMicrotask(() => order.push("qm2"));
+    setTimeout(() => {
+      expect(order).toEqual(["qm1", "p", "qm2"]);
+      done();
+    }, 0);
+  });
+});