This is a tried and true method to avoid a situation in which you want to make a call to a static url which may return a different result each time. Simply append an argument to the url with a random or otherwise unique string as the value.
This will return a unique string every time that you call it.
Now, suppose you are calling a url that looks like this:
var url = "http://myserver.com/getSomeImage";
It may work the way you expect in one browser but not in another. Just append an argument to it like so:
var url = "http://myserver.com/getSomeImage?cacheKiller=" + getUniqueString();
The url might look like this: