Google Chrome extension modifying page request

Is it possible to catch the request of a page before it is sent out? I would like to check and modify the data sent out. For example if I have a text box on a page and the form was submitted I would like to get to the data of the text box using the extension modify it and the开发者_Go百科n send it on it's way.

If any one can point me in the right direction that would be grate

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Chrome has chrome.experimental.webRequest API module which allows to catch web requests before they are sent, but from the docs it doesn't look like you can modify them, just observe.

I think you would be better off injecting a content script to pages and listening to onbeforesubmit event on forms.