Pretty straightforward for people who've worked on setTimeouts and setIntervals before.
<ol>
<li><code>setInterval</code> can be implemented as repeated <code>setTimeouts</code>.</li>
<li>First call with be done after <code>delay</code></li>
<li>Subsequent calls after <code>delay + period * count</code> millisecs</li>
<li>Generate a numeric timer id every time <code>mySetInterval</code> is called (along with the
associated real timeouts) and store them in the function object property.</li>
</ol>
<pre class="shiki github-dark shaku"><code>/** * @param {Function} func * @param {number} delay * @param {number} period * @return {number} */function mySetInterval(func, delay, period) { // your code here let count = 0; // Store a map of numeric interval ids in the function object itself if (!mySetInterval.timers) { mySetInterval.timers = {}; } // Generate numeric interval id const timerId = mySetInterval.timers.length + 1; // Recursive setTimeout function timeoutFn() { func(); mySetInterval.timers[timerId] = setTimeout( timeoutFn, delay + period * (++count) ); } mySetInterval.timers[timerId] = setTimeout(timeoutFn, delay); return timerId;}/** * @param { number } id */function myClearInterval(id) { clearTimeout(mySetInterval.timers[id]);}</code></pre>

Easy to understand solution, with comments