setInterval

Learn to run code repeatedly at an interval with setInterval.

Repeating call with setInterval

setInterval runs a function repeatedly at a fixed interval. The second parameter is again in milliseconds.

setInterval(() => {
  console.log('Tick');
}, 1000);

This code logs Tick every second. Unlike setTimeout, the callback is called not once but again and again. The timer keeps running until you stop it with clearInterval. As long as the page is open, the interval repeats forever.

Building a counter with setInterval

Inside setInterval you can increase a variable to build a counter. On each call the variable grows by one and you write the result into an element.

const counter = document.querySelector('#counter');
let count = 0;
setInterval(() => {
  count = count + 1;
  counter.textContent = count;
}, 1000);

This code increases count by one every second and writes it into the #counter element. As long as the page is open, the counter grows forever. To stop it you need clearInterval; we will see it in the next lesson.

Exercise Increase the counter element by 1 every second

Increase a #counter element by 1 every second with setInterval. Increase the count variable and write it to counter.textContent.

Show example solution

const counter = document.querySelector('#counter');
let count = 0;
setInterval(() => {
  count = count + 1;
  counter.textContent = count;
}, 1000);

Test yourself

What is the difference between setInterval and setTimeout?
- setInterval runs the callback repeatedly, setTimeout once
- setInterval is faster
- setTimeout is only for delays
- They are the same
Show answer

setInterval runs the callback repeatedly, setTimeout once — Correct! setInterval calls the callback again and again; setTimeout only once.

Complete the setInterval call

setInterval(() => {
  console.log('Tick');
}, ____);

Show answer

setInterval(() => {
  console.log('Tick');
}, 2000);

Match the setInterval parts

setInterval

repeating timer
callback

runs every interval
1000

1 second interval
count = count + 1

increases counter by one

Next lesson: Stopping with clearInterval

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies