>When making a GET call via jQuery.ajax, jQuery 1.2.1 adds a URL >parameter named '_' (the single underscore character) whose value is >the current time stamp. I'm not sure I understand why, and in any >case, this caused me some grief when I tried to use it in a Facebook >app. The reason is that the Facebook API requires a "signature" >parameter as part of each request, and this parameter is basically the >MD5 hash of the rest of the parameters. So the extraneous jQuery >parameter was not being accounted for in my code, causing Facebook to >complain about an incorrect signature. > >Perhaps someone can explain the need for this parameter. And perhaps >it can be made optional in a future release?
This is done to prevent AJAX requests from being cached. The only way to ensure client-side code invokes a new request is to add a timestamp signature as a URL parameter. This will make browsers request the document again from the server. -Dan
