<pre class="shiki github-dark shaku"><code>class FakeTimer { constructor() { this.timerId = 0; this.queue = []; this.currentTime = 0; this.activeIntervals = new Map(); } install() { this.origins = { dateNow: Date.now, setInterval: window.setInterval, clearInterval: window.clearInterval, }; window.setInterval = (cb, time, ...args) =&gt; { const id = this.timerId++; this.activeIntervals.set(id, time); this.queue.push({ id, cb, args, time: this.currentTime + time, intervalTime: time, }); this.queue.sort((a, b) =&gt; a.time - b.time); return id; }; window.clearInterval = (removeId) =&gt; { this.activeIntervals.delete(removeId); }; Date.now = () =&gt; this.currentTime; } uninstall() { Date.now = this.origins.dateNow; window.setInterval = this.origins.setInterval; window.clearInterval = this.origins.clearInterval; } tick() { while (this.queue.length &gt; 0) { const { id, cb, args, time, intervalTime } = this.queue.shift(); this.currentTime = time; cb(...args); if (this.activeIntervals.has(id)) { this.queue.push({ id, cb, args, time: this.currentTime + intervalTime, intervalTime, }); this.queue.sort((a, b) =&gt; a.time - b.time); } } }}</code></pre>

My solution

This is a follow-up on 36. create a fake timer(setTimeout) Like setTimeout, setInterval also is not accurate. (please refer Event Loop for detail). Th…