Event handler when site doesn't match manifest.json 'matches' - google-chrome-extension

Question

My manifest.json contains this block:
"content_scripts": [
{
"all_frames": true,
"matches": [
"*://www.google.com/*",
"*://www.cnn.com/*",
"*://*.foxnews.com/*"
],
"js": ["js/main.js"]
}
],
I need an event to fire (either in my content js or background.js, doesn't matter) whenever the user visits a website that does not match one of the sites in my matches setting.
How is it done?

Answer 1

In your background.js you could add a listener for tab load. In this you could fetch the URL of the current tab and match with a list.
chrome.tabs.onUpdated.addListener(function(tabId, info, tab) {
if (info.status == "complete") {
var url = tab.url.replace(/.*?:\/\//g, "").replace(/\/$/, ""); //removes the protocol
var allowedURLS = ["www.google.com", "www.cnn.com", "foxnews.com"];
for(var i in allowedURLs) {
if(allowedURLs[i].indexOf(url) == -1) {
//URL does not match
break;
}
}
}
});

Answer 2

You need to use exclude_matches in your content script , that says that the script under it will not inject.
From the google documentation:
Excludes pages that this content script would otherwise be injected into. See Match Patterns for more details on the syntax of these strings and Match patterns and globs for information on how to exclude URLs.
For your case:
"content_scripts": [
{
"all_frames": true,
"matches": ["<all_urls>"],
"js": ["js/main.js"],
"exclude_matches": [
"*://www.google.com/*",
"*://www.cnn.com/*",
"*://*.foxnews.com/*",
]
}
]