How can I programmatically block sites through the Chrome browser?
My idea is to do it through a custom extension, so I think it would be implemented in JavaScript.
I think it's as simple as redirecting from the page the user enters to a custom error page -- but I'm not sure exactly how to go about doing this (I haven't really done Chrome extensions before)
You should look into chrome.webRequest
and its samples.
They will achieve exactly what you need: you detect an attempt to open a page in onBeforeRequest
in your background script, analyze the request and optionally redirect it to your page implementing your logic.
See CatBlock sample here for a starting point.