What's the purpose of this Javascript variable?

What does this do, and why is it declared this way?

   var shroom = 'data:image/gif;base64,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开发者_如何学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%3D%3D';

It represents a GIF image encoded in base 64.

http://en.wikipedia.org/wiki/Data_URI_scheme

It's a Data URI, which is a file encoded in a URL. More info can be found on wikipedia. Here's an online tool used to create them: http://software.hixie.ch/utilities/cgi/data/data

I believe IE doesn't have total support for Data URIs, so they're not too commonly used. If IE did, though, they'd be great for icons and small graphics embedded right into style sheets.

Here is a link to encode base 64 with Javascript

Base 64 with Javascript