Javascript to select randomly different code


I am currently designing a site, and on it there will be affiliate advertising. As i have many different affiliates i want the page to randomly select one of these affiliates’ adverts to show in the places that i have designated. Each affiliate has given me some code to drop in to my html page. I was wondering if there was some javascript that would select randomly one of these bits of code and display it on the page load, in effect removing the need for me to continually have to manually update and change the code so that it shows a rotation of these adverts.

I imagine that it would be some sort of script that reads from an array (this array has each different advert code in it). If anyone could help me it would be much appreciated!

Many thanks