What is the code to JavaScript preload images?

The following code is handy for JavaScript preloading a single image:

<SCRIPT language="JavaScript">
    picture=new Image;
    picture.src="http://whadiz.com/images/logo1.gif";
</SCRIPT>

You first need to define an image and then the source of the image. You can also define explicit width and height attributes for the image, for example:

picture=new Image(100,25);

Does all browsers support JavaScript preload images?

JavaScript preload images is dependant on the browser's ability to create and manipulate an Image object.

To make sure a browser has this ability, you may wish to add a test as follows:

<SCRIPT language="JavaScript">
if (document.images) {
    picture=new Image;
    picture.src="http://whadiz.com/images/logo1.gif";
}
</SCRIPT>

Where should I place the JavaScript preload images code?

The ideal place to put the JavaScript preload images code would be in the HEAD section of your HTML.