How to send an alert in chrome extensions?

Question

I am trying to get some experience with chrome extensions. I have a question though. Let's say I am writing an extension that everytime you see the word (wow) in the url, i will alert the user with a red page that they have to click on accept to pass, or an alert box that they have to get through in order to see the page, how would i:

1) get the url of the page 2) make the red alerting page, or the alert box without the need for the user to actually go click at the extension's icon to get information?

Thank you so much

Answer 1

It's certainly late, but I thought I'd answer anyway. What you need is a content script. You can set it to match on certain domains and then do a more granular filter inside the script checking against window.location and alerting/displaying a div layer for matched URLs. The content script has full access to the page DOM so you can easily hide or dim it and show a warning.