One of the bugs features of Internet Explorer is it’s insistence on caching anything and everything. IE caching has cost me many hours of debugging time since I started doing Ajax development last year.

My most recent problem was a form I had that described an image. I would modify one of the fields in this form and save it, but the change didn’t reflect when I reloaded the page. After ruling out the PHP code and the database as the source of the bug, I did some research about caching in IE (since this problem didn’t occur in any other browser).

What I found was that you have to be careful when making ajax GET requests in IE. If you make a request to a URL with the same query string as another request made recently, IE figures that the page won’t have changed, so it pulls it from cache. Once I found this, it was a snap to avoid the problem.

There are two ways to handle this. One is to use POST request all the time. I don’t like to do this unless I’m submitting a form, so I use the second method which is to make the GET query string unique. I do this by adding a random string at the end:

http = createRequestObject();
var d = new Date();
var time = d.getTime();
var url = 'library.php?' + action + '&time=' + time;
http.open('GET', url,true);
http.onreadystatechange = handleResponse;
http.send(null);

This way, IE will never try to use a cached copy of your page.