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.