# Stopping a timer in JavaScript

You already know how to start a timer, now let's learn how to stop it. To do this, you need to know that each timer started with the `setInterval` function has a unique number. This number is returned by the `setInterval` function when the timer starts:

`let timerId = setInterval(function() { console.log('!') }, 1000); alert(timerId); // will display the number of the timer`

To stop the timer, use the `clearInterval` function, which takes a unique number of the timer to be stopped.

For example, let's start a timer that prints numbers to the console in ascending order, starting with `1`. Let's stop the timer as soon as the number `10` is displayed on the screen:

`let i = 0; let timerId = setInterval(function() { console.log(++i); if (i >= 10) { clearInterval(timerId); } }, 1000);`

Let a variable be given that initially stores the number `10`. Start a timer that every second will decrease the value of this variable by `1` and print this value to the console. As soon as the value of the variable reaches zero, stop the timer.

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