feat(esl-utils): utility to postpone execution to microtask

src/modules/esl-utils/async.ts

@@ -3,4 +3,5 @@ export * from './async/promise';
 export * from './async/raf';
 export * from './async/debounce';
 export * from './async/throttle';
+export * from './async/microtask';
 export * from './async/delayed-task';

src/modules/esl-utils/async/microtask.ts

@@ -0,0 +1,15 @@
+/**
+ * A decorator utility to postpone callback execution once after the main task execution
+ * (as a microtask produced with Promise)
+ */
+export function microtask<T>(fn: (...arg: [T?]) => void, thisArg?: object): (arg?: T) => void {
+  const args: T[] = [];
+  return function microtaskFn(arg: T): void {
+    args.push(arg);
+    if ((microtaskFn as any).request) return;
+    (microtaskFn as any).request = Promise.resolve().then(() => {
+      delete (microtaskFn as any).request;
+      fn.call(thisArg || this, args);
+    });
+  };
+}

src/modules/esl-utils/async/test/microtask.test.ts

@@ -0,0 +1,26 @@
+import {microtask} from '../microtask';
+
+describe('sync/microtask', () => {
+  test('Decorated as microtask callback call does not lead to original function immediate execution', () => {
+    const fn = jest.fn();
+    const decorated = microtask(fn);
+    for (let i = 0; i < 5; i++) decorated();
+    expect(fn).toBeCalledTimes(0);
+  });
+  test('Decorated as microtask callback called once the macrotask done', async () => {
+    const fn = jest.fn();
+    const decorated = microtask(fn);
+    for (let i = 0; i < 5; i++) decorated();
+    await Promise.resolve();
+    expect(fn).toBeCalledTimes(1);
+  });
+  test('Decorated as microtask callback receives a list of call arguments', async () => {
+    const fn = jest.fn();
+    const decorated = microtask(fn);
+    const params = [Symbol('Arg 1'), Symbol('Arg 2'), Symbol('Arg 3')];
+
+    for (const param of params) decorated(param);
+    await Promise.resolve();
+    expect(fn).toBeCalledWith(expect.arrayContaining(params));
+  });
+});