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.

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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.

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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

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It must be there to prevent caching.

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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.

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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).