How To Slow Down A For-Loop in JavaScript

How To Slow Down A For-Loop in JavaScript

Yes, it’s possible due to a simple trick. For loops are indispensable. They help us to program sequences.

For loops are indispensable. They help us to program sequences.

But there is one problem with them — the for loop runs through as fast as possible. If we iterate through an array, this is, of course, desirable.

But if we do, e.g., requests in the loop, this can lead to problems.

It would be nice if each loop's execution takes a fixed time interval — for example, one pass per second.

I will show you how to do this — here is how to time a for-loop.

First — how it does not work

If you’re looking for a direct solution to your problem, feel free to skip this part. If you want to learn something about JS, then stay for a moment.

I want to explain why common solutions don’t work.

Thanks to setTimeout,d we can specify that a certain code should be executed only after x-time. This sounds like the solution to our problem. Just put the timeout in the for-loop, and the loop is less fast:

for (let i = 0; i < 100; i++) {
      setTimeout(() => {
        console.log(i)
      }, 1000)
    }

When we run the code with setTimeout, the following happens:

nothing happens for 1 second; then all the logs come up in a flash.

Not really what we had hoped for.

The reason for this is a small error in thinking. It seems like the timeout doesn’t apply to every element — yes, it does.

But we forget how JavaScript executes code. The loop creates all timeouts immediately, not sequentially. Of course, this is very fast — so all timeouts have almost the same start time.

As soon as the time is up, the logs are made — all at once.

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