<pre class="shiki github-dark shaku"><code>class FakeTimer { constructor() { this.origin = { dateNow: Date.now, setTimeout: window.setTimeout, clearTimeout: window.clearTimeout } this.queue = [] this.id = 1 this.currentTime = 0 } install() { // replace window.setTimeout, window.clearTimeout, Date.now // with your implementation window.setTimeout = (cb, timer, ...args) =&gt; { const id = this.id++ this.queue.push({ id, cb, time: timer + this.currentTime, args }) this.queue.sort((a, b) =&gt; a.time - b.time) return id } window.clearTimeout = id =&gt; { this.queue = this.queue.filter(item =&gt; item.id !== id) } Date.now = () =&gt; this.currentTime } uninstall() { // restore the original implementation of // window.setTimeout, window.clearTimeout, Date.now window.setTimeout = this.origin.setTimeout window.clearTimeout = this.origin.clearTimeout Date.now = this.origin.dateNow } tick() { // run the scheduled functions without waiting while(this.queue.length) { const { cb, time, args } = this.queue.shift() this.currentTime = time cb(...args) } }}</code></pre>

This is my answer

setTimeout adds task in to a task queue to be handled later, the time actually is no accurate. (Event Loop). This is OK in general web application, bu…