How To Preload Images In JavaScript

Usually high resolution images can really slow down the website. images are loaded only after an HTTP request is sent for them, either passively via an <img> tag or actively through a method call. Preloading images comes to our rescue which means loading an image into cache before being used. The simplest way to preload an image is to instantiate a new Image() object in JavaScript and pass it the URL of the image you want preloaded.

The following example demonstrates the preloading of images:

JavaScript Preload Images Example

<!DOCTYPE html>
<TITLE>Example- preloading of images</TITLE>
<script language = "JavaScript">
function preloader()
heavyImage = new Image();
heavyImage.src = "image.jpg";
<body onLoad="javascript:preloader()">
     <a href="#" onMouseOver="javascript:document.image.src='image.jpg'">
     <img name="img01" src="image.jpg"></a>

Note that the image tag does not itself handle onMouseOver() and onMouseOut() events. Hence <img> tag in the example above has been enclosed in an <a> tag, which does include support for those event types.

Preload Images In JavaScript Demo

  • Save the file as preloading.html in your system.
  • Just open the file in the browser, you will notice how the image gets loaded fast.

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