getting related js files: What is the point of adding ?t=B48E5AB

I'm using CKEditor which is a multi-file library so the main js file calls other js and css files. I'm noticing that after the main file is called, additional files have a ?t=CODE added to them, so something like this, but the actual files don't have that extra ?t=B49E5B开发者_如何学GoQ at the end.

http://site.com/ckeditor/config.js?t=B49E5BQ
http://site.com/ckeditor/extra.js?t=B49E5BQ

What's the point of this

P.S. Please feel free to add additional tags, because I'm not sure about this one.

This sort of trailing data is sometimes put into URLs for resources files like scripts/stylesheets so as to prevent caching of resources across re-deployments.

Whenever you change a resource, you change the code in HTML files/templates which require that resource, so that clients re-request the resource from the server the next time they load the page.

I would guess that the URL parameter is added to bypass any caching mechanisms. When a client sees the same URL with a different query parameter, that usually means the client can't use the cached version of the resource (in this case a JS file) and go to the server to fetch the latest version.

In HTTP, if a URL is the same in every way except for the URL parameters, a client can not assume that those files/resources are the same resulting object.

Which means:

http://site.com/ckeditor/config.js?t=B49E5BQ

is not the same as:

http://site.com/ckeditor/config.js?t=1234

It must be there to prevent caching.

I do this occasionally for images and script files. In my case, it's a meaningless argument (usually datetime) that just forces the browser to fetch a new copy every time.

If the parameter keeps changing, those files won't be cached on the client side.

Often this is easier than say, changing the name of the file to include a version number (jquery-1.6.2.js works nicely, but do you want to rename config.js to config-1.0.js, -2.0, etc. every time you make a change?

Like all the other answers, this simply forces the browser to grab the latest version when the querystring (?t=B49E5BQ) is changed. In our case, we simply add the date (?06022011).