perf: uses setImmediate() implementation from tiny-set-immediate

package.json

@@ -64,5 +64,8 @@
     "sinon": "^7.2.7",
     "sinon-chai": "^3.3.0",
     "typescript": "^3.9.5"
+  },
+  "dependencies": {
+    "tiny-set-immediate": "^1.0.2"
   }
 }

taskscheduler.ts

@@ -1,15 +1,13 @@
+import { setImmediate } from 'tiny-set-immediate';
+
 const resolved = Promise.resolve(undefined);
 
 // Returns a function that asynchronously schedules a task
-export function createTaskScheduler() : TaskScheduler {
+export function createTaskScheduler(scheduleMacrotask: TaskScheduler = setImmediate) : TaskScheduler {
   // Use or create a microtask scheduler
   const scheduleMicrotask = typeof queueMicrotask === 'function' ?
     queueMicrotask : (task: Task) => resolved.then(task);
 
-  // Use or create a macrotask scheduler
-  const scheduleMacrotask = typeof setImmediate === 'function' ?
-    setImmediate : (task: Task) => setTimeout(task, 0);
-
   // Interrupt with a macrotask every once in a while to avoid freezing
   let i = 0;
   let queue: Task[] | null = null;

test/TaskScheduler-test.js

@@ -51,28 +51,27 @@ describe('TaskScheduler', () => {
     });
   });
 
-  describe('a task scheduler when setImmediate exists', () => {
+  describe('a task scheduler using an externally-provided setImmediate() implementation', () => {
     const backups = {};
+    let setImmediate = sinon.spy();
 
     beforeEach(() => {
       backups.setTimeout = global.setTimeout;
       backups.queueMicrotask = global.queueMicrotask;
-      backups.setImmediate = global.setImmediate;
-      global.setImmediate = sinon.spy();
       global.setTimeout = sinon.spy();
       global.queueMicrotask = sinon.spy();
+      setImmediate = sinon.spy();
     });
 
     after(() => {
       global.setTimeout = backups.setTimeout;
       global.queueMicrotask = backups.queueMicrotask;
-      global.setImmediate = backups.setImmediate;
       delete global.window;
     });
 
     it('alternates between setImmediate and queueMicrotask', () => {
       // Perform 100 calls
-      const taskScheduler = createTaskScheduler();
+      const taskScheduler = createTaskScheduler(setImmediate);
       const tasks = [];
       for (let i = 0; i < 100; i++) {
         tasks[i] = sinon.spy();
@@ -83,11 +82,11 @@ describe('TaskScheduler', () => {
       expect(global.setTimeout).to.have.callCount(0);
 
       // 99 calls should have gone to queueMicrotask, 1 to setImmediate
-      expect(global.setImmediate).to.have.callCount(1);
+      expect(setImmediate).to.have.callCount(1);
       expect(global.queueMicrotask).to.have.callCount(99);
 
       // When the setImmediate callback is invoked, the final call should to through
-      global.setImmediate.getCall(0).callback();
+      setImmediate.getCall(0).callback();
       expect(global.queueMicrotask).to.have.callCount(100);
 
       // Verify all microtasks were scheduled
@@ -97,7 +96,7 @@ describe('TaskScheduler', () => {
 
     it('waits for setImmediate to finish before calling queueMicrotask', () => {
       // Perform 150 calls
-      const taskScheduler = createTaskScheduler();
+      const taskScheduler = createTaskScheduler(setImmediate);
       const tasks = [];
       for (let i = 0; i < 150; i++) {
         tasks[i] = sinon.spy();
@@ -108,11 +107,11 @@ describe('TaskScheduler', () => {
       expect(global.setTimeout).to.have.callCount(0);
 
       // 99 calls should have gone to queueMicrotask, 1 to setImmediate
-      expect(global.setImmediate).to.have.callCount(1);
+      expect(setImmediate).to.have.callCount(1);
       expect(global.queueMicrotask).to.have.callCount(99);
 
       // When the setImmediate callback is invoked, the final call should to through
-      global.setImmediate.getCall(0).callback();
+      setImmediate.getCall(0).callback();
       expect(global.queueMicrotask).to.have.callCount(150);
 
       // Verify all microtasks were scheduled
@@ -121,48 +120,6 @@ describe('TaskScheduler', () => {
     });
   });
 
-  describe('a task scheduler when setImmediate does not exist', () => {
-    const backups = {};
-
-    before(() => {
-      backups.setTimeout = global.setTimeout;
-      backups.queueMicrotask = global.queueMicrotask;
-      backups.setImmediate = global.setImmediate;
-      global.setImmediate = undefined;
-      global.setTimeout = sinon.spy();
-      global.queueMicrotask = sinon.spy();
-    });
-
-    after(() => {
-      global.setTimeout = backups.setTimeout;
-      global.queueMicrotask = backups.queueMicrotask;
-      global.setImmediate = backups.setImmediate;
-      delete global.window;
-    });
-
-    it('alternates between setTimeout and queueMicrotask', () => {
-      // Perform 100 calls
-      const taskScheduler = createTaskScheduler();
-      const tasks = [];
-      for (let i = 0; i < 100; i++) {
-        tasks[i] = sinon.spy();
-        taskScheduler(tasks[i]);
-      }
-
-      // 99 calls should have gone to queueMicrotask, 1 to setTimeout
-      expect(global.setTimeout).to.have.callCount(1);
-      expect(global.queueMicrotask).to.have.callCount(99);
-
-      // When the setTimeout callback is invoked, the final call should to through
-      global.setTimeout.getCall(0).args[0]();
-      expect(global.queueMicrotask).to.have.callCount(100);
-
-      // Verify all microtasks were scheduled
-      for (let i = 0; i < 100; i++)
-        expect(global.queueMicrotask).to.have.been.calledWith(tasks[i]);
-    });
-  });
-
   describe('a task scheduler when queueMicrotask is unavailable', () => {
     const backups = {};
 
@@ -176,7 +133,7 @@ describe('TaskScheduler', () => {
     });
 
     it('can schedule a task', done => {
-      const taskScheduler = createTaskScheduler();
+      const taskScheduler = createTaskScheduler(setImmediate);
       taskScheduler(done);
     });
   });

tsconfig.json

@@ -39,7 +39,7 @@
     "noFallthroughCasesInSwitch": true,       /* Report errors for fallthrough cases in switch statement. */
 
     /* Module Resolution Options */
-    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
+    "moduleResolution": "node",               /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
     // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
     // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
     // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */