JavaScript setTimeout

On my homepage, instead of having just one image I have used Javascript to create a setTimeout to give my home page a changing image every 5 seconds.

I have also linked this javascript to my home page through an external javascript document.


"var currentImgNumber = 1;
var numberOfImages = 4;
function window_onload()
{
setTimeout("switchImage()",5000);
}

function switchImage()
{
currentImgNumber++;
document.imgAdvert.src = 'AdvertImage' + currentImgNumber + '.jpg';
if (currentImgNumber < numberOfImages)
{
setTimeout("switchImage()",5000); }
}"

This is my code showing how the timer works