Error in launching Chrome Extension for a specific page

Question

I'm writing a simple Chrome extension that displays a JavaScript alert saying "Hello World". In this example I have specified that the extension will only run for google.com (by putting this in the permissions property within manifest.json).

Even after everything in the target page has loaded, the alert doesn't appear. Here is my script so far:

File: manifest.json

{   "name": "Hello",   "version": "1.0",   "description": "Says hello to Google",   "permissions": ["http://*.google.com/"]   "browser_action": {     "popup": "Hello.html"   } } 

File: Hello.html

<script language="Javascript">    alert("Hello World"); </script> 

Answer 1

You are adding a browser action popup, which adds a button to the top-right of your browser. (It's probably invisible because you haven't specified an image for it. There should be some empty space to the right of your address bar; try clicking it to see your Hello.html in a popup.)

What you want is a content script. Content scripts can get injected into every page that Chrome loads. You can use the matches and exclude_matches sub-items in your manifest file to specify which pages get your injected script.

{   "name": "Hello",   "version": "1.0",   "description": "Says hello to Google",   "permissions": ["tabs", "*://*.google.com/*"],   "content_scripts": [     {       "matches": ["*://*.google.com/*"],       "js": ["hello.js"]     }   ] } 

Make sure you rename Hello.html to hello.js (and get rid of the <script> tags).

Note also that I changed your http://*.google.com/ to *://*.google.com/* so that it will apply to Google over HTTP and HTTPS (and the trailing * ensures that it will apply to all pages on google.com, not just the main page).