Set Interval

The setInterval method is used to call a function and add a delay time to it, in milliseconds, before the function will run again. For example, if you're making a function that generates a random color, you can use setInterval() to say how long the computer has to wait before the function runs again and generates another color. This is useful in making functions repeat.

The first parameter in the method is the name of the function for which you're setting an interval. The second parameter specifies the duration of the interval. You can also add additional parameters if you want to pass arguments to the function.

As another simple example, let's create a function called repeatSaying where it says "And again!" every 2 seconds in the console.

function repeatSaying() {
console.log("And again");
}
//when called, it generates in the console: "And again!"

setInterval(repeatSaying, 2000);
//calls the function every 2 seconds

You can also add parameters of a function when you use set interval. Continuing on with the previous example let's add an ellipsis to the console statement, to show that it repeats. First we'll add a parameter called el which is short for ellipse. Next we'll add a + followed by calling are parameter el to show that the value of the parameter comes after. Finally in set interval let's add a comma , followed by a string for the value of the ellipse parameter, we'll put "...".

function repeatSaying(el) {
console.log("And again!" + el);
}

setInterval(repeatSaying, 2000, "...");
//When it runs, it'll repeat the saying "And again!..."

As you can see from this example, after you put the function and interval for the function, you can set the values of the function parameters inside set interval.

Clear Interval

You can use the clearInterval() method to remove a set interval with a specefic variable name. As an example based on the previous one let's store set interval into a variable named intervalTime, however, right after our variable we'll call it inside clear interval by writing clearInterval(intervalTime).

function repeatSaying(el) {
console.log("And again!" + el);
}

var interval = setInterval(repeatSaying, 2000, "...");

clearInterval(interval);
//The clear Interval method stops setInterval

When this code is run, you'll see that there is no output. This is because setInterval was the only thing calling the repeatSaying function, but since it was removed by clearInterval it's no longer is called. Even if it was called seperately using repeatSaying() it would only run once because clear Interval stops it from repeating.