<pre class="shiki github-dark shaku"><code>class FakeTimer { constructor(){ this.setTimer = window.setTimeout; this.clearTimer = window.clearTimeout; this.setDate = window.Date.now; this.timers = []; this.currentTime = 0; } install() { // replace window.setTimeout, window.clearTimeout, Date.now // with your implementation window.setTimeout = (callback, ms=0) =&gt;{ const timerId = Symbol(); this.timers.push({ ms: this.currentTime+ms, callback, timerId: timerId }); this.timers.sort((a,b) =&gt; a.ms - b.ms); return timerId; } window.clearTimeout = (timerId) =&gt; { this.timers = this.timers.filter(timer =&gt; { return timer.timerId !== timerId }); } Date.now = () =&gt; { return this.currentTime; } } uninstall() { // restore the original implementation of // window.setTimeout, window.clearTimeout, Date.now window.setTimeout = this.setTimer; window.clearTimeout = this.clearTimer; window.Date.now = this.setDate; } tick() { while (this.timers.length) { const timer = this.timers.shift(); this.currentTime = timer.ms; timer.callback(); } }}</code></pre>

solution

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…