In one of my recent interview I was asked to implement setInterval.
Here is the question definition:
Let's assume there is no setInterval available to us, but you do have setTimeout and using setTimeOut you have to implement setInterval. It should satisfy these two conditions:
- It should be able to take
callbackanddelayas parameter. - There should be a way to clear the
interval.
This is what I was able to come up with (NOTE: This is a brushed up code similar to what I wrote in interview):
function mySetInterval(callback, delay) {
let clears = [];
// NOTE: A recursive function which gets called after **delay**
(function recFun() {
clears.push(setTimeout(() => {
callback();
recFun();
}, delay));
}())
return () => {
for (let i = 0; i < clears.length; i++) {
clearTimeout(clears[i]);
}
};
}
// To Test
let count = 1;
let clear = mySetInterval(() => {
console.log("hello world", count++);
}, 1000);
setTimeout(() => {
clear();
}, 5000);
There might/will be different ways to solve this, the one thing that I love about the above code is, it gives a practical example of using closures in javascript.
If you have any other way to solve it or you find something wrong with above, please do let me know me in comments.
Approach II: This can handle multiple setInterval
(function(window) {
let interval = {}
window.setInterval = function(fun, delay) {
let rndId = Math.floor(Math.random() * 1000);
const execute = function() {
let id = setTimeout(() => {
fun();
execute();
}, delay)
if (!interval[rndId]) {
interval[rndId] = []
}
interval[rndId].push(id)
console.log(rndId, interval[rndId])
}
execute();
return rndId;
}
window.clearInterval = function(rid) {
console.log("Rid and Interval", rid, interval)
while (interval[rid].length > 0) {
console.log(interval[rid])
clearTimeout(interval[rid].pop());
}
}
}(window))
const pid = setInterval(() => {
console.log("Hello world");
}, 2000);
console.log("PID", pid)
setTimeout(() => {
clearInterval(pid)
}, 10000)
-- Thanks, Ravi
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