<pre class="shiki github-dark shaku"><code>class FakeTimer { tasks = new Map(); seconds = 0; install() { // replace window.setInterval, window.clearInterval, Date.now // with your implementation this.setIntervalOriginal = window.setInterval; this.clearIntervalOriginal = window.clearInterval; this.dateNow = Date.now; window.setInterval = (func, freq) =&gt; { const intervalId = this.tasks.size + 1; this.tasks.set(intervalId, [func, freq + this.seconds]); return intervalId; }; window.clearInterval = (id) =&gt; { this.tasks.delete(id); }; Date.now = () =&gt; this.seconds; } uninstall() { // restore the original implementation of // window.setInterval, window.clearInterval, Date.now window.setInterval = this.setIntervalOriginal; window.clearInterval = this.clearIntervalOriginal; Date.now = this.dateNow; } tick() { // run the scheduled functions without waiting while (this.tasks.size) { let firstTaskId; for (const [taskId,[fn,freq]] of this.tasks) { if (firstTaskId === undefined || this.tasks.get(firstTaskId)[1] &gt; freq) { firstTaskId = taskId; } } let [fn, freq] = this.tasks.get(firstTaskId); this.seconds = freq; fn(); if (this.tasks.has(firstTaskId)) { this.tasks.get(firstTaskId)[1] = this.seconds + freq; } } }}</code></pre>

Very similar to setTimeout problem #36

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…