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Using a Timer in Javascript


In my previous project Changing Image Source, we change images by clicking. But what if we want to change them automatically and continuously?

We have to use a timer on it. With just few lines of codes added in our previous project, we can make it work.

  1. var timer = setInterval('changeImg()', 3000);

We will use setInterval method. Inside of it is the 2 arguments. First is the code that you want to run, and second is the speed.

You can also use setTimeout instead of setInterval but the difference is that setTimeout execute once while setInterval execute the code repeatedly.

Then, if you want to stop the timer, you can use clearInterval method. This will stop the interval from running. As you can see in our code, we give the timer a variable name. We can use this in clearInterval.

  1. clearInterval(timer);

We can put this on our onClick event:

  1. <img src="images/chrome.jpg" id="browser" onClick="clearInterval(timer);">

The interval will stop when the user clicked the image.

Hope you learn from this.

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