Google chrome frame - how does it work?

I'm looking into chrome frame and I'm wondering how it works.... http://scriptsrc.net shows that it's a javascript that can be embedded on the page....

http://code.google.com/c开发者_高级运维hrome/chromeframe/ shows it as an install file... does the JS prompt for an installation or something?

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Google chrome frame is a plugin (think Adobe Flash) for Internet Explorer, that replaces core modules of IE (unlike Flash), like layout/rendering and javascript. But the UI remains. Then there is some javascript that can detect if this is real IE or IE+Chrome, and also offer an install option to the user. Also there is a HTTP-header and a meta-tag that are required to switch IE to chrome mode, when available.

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The JavaScript is to detect it and enable it if it's there. (scriptsrc is just giving you the link to the file, which is on the Google CDN.) The end user does have to do a one-time install of it, it's a plug-in (like Flash or Java). Quoting from this page in the Google documentation:

In Internet Explorer, check() determines if Chrome Frame is installed. If not, the user is prompted to install it.