How to cancel a setTimeout in JavaScript

#javascript

setTimeout in JavaScript is a native function that sets a function to be executed when a specified timer completes.

Here's the syntax:

setTimeout(function, timer)

timer is in milliseconds. Here's an example where we do something after two seconds:

setTimeout(() => {
  console.log("hey...I'm 2 seconds in")
}, 2000}

Cancelling a setTimeout

You may not want a setTimeout to complete for various reasons. One reason can be cleaning up side-effects in React useEffect. So how do you stop it? Here's how...

The setTimeout function returns an id when declared:

const timeoutId = setTimeout(() => {}, 1000)

With this id and the clearTimeout JavaScript function, you can cancel a setTimeout.

Here's the syntax of the clearTimeout function:

clearTimeout(timeoutId)

With this, we can have:

const timeoutId = setTimeout(() => {
  console.log("hey...I'm 2 seconds in"
}, 2000}

// later on

clearTimeout(timeoutId)

If the setTimeout declaration has not been completed, the clearTimeout function will cancel it, and the callback function will not be executed anymore.

Latest comments (5)

Laurent • Oct 4 '23

Thanks for this consise summary. In addition to this, would you know whether a setTimeout is discarded automatically by the system when the given duration is reached or still exists after?