What causes a query string when requesting jQuery? e.g. /jquery-1.3.2.min.js?_=12553...

Question

I'm troubleshooting a jQuery problem which happens when the HTTP requests for a page load include this query string:

GET /Scripts/jquery-1.3.2.min.js?_=1255309685187

Normally, the request has no query string and the response status code is 304:

GET /Scripts/jquery-1.3.2.min.js

However, every so often a query string is appended. Where does this query string come from? What does it mean?

The webserver is Visual Studio's Development Server, and I usually see this in IE8. Occasionally I'll see it in Firefox though. The app is ASP.NET MVC.

Answer 1

looks like the number after is a unix time. i don't know why this would be automatically appended tho.

possibly some way of getting around browser cache? forcing a reload of the js basically?

Answer 2

Generally such a value is a TIMESTAMP representation appended as a query string to ensure that the file you are requesting, in this case jquery-1.3.2.min.js, is not cached. The unique query string is strictly used for purposes of grabbing the newest version of the file, not one found in your browser cache.