Chrome Extension - Simple Content Script for running js on any page

Question

How can I write a simple Chrome Extension content script that will execute JavaScript (for example alert("hello");) on every page load?

So when I navigate to a page or reload a page, the JavaScript should run.

This is my manifest.json file so far:

{     "name": "Highlight some phrases",     "description": "Hightlight some pre defined text from websql database after page loads",     "version": "0.1",     "permissions": [         "tabs","<all_urls>"     ],     "browser_action": {         "default_icon": "icon.png",         "default_popup": "popup.html"     },      "content_scripts": [         {         "matches": [             "http://*/*",             "https://*/*"         ],         "js": ["content.js"]         }     ],      "background": {         "page": "background.html"      },      "manifest_version": 2 } 

Answer 1

If all you need is to alert hello on every page load or reload, below is a simple demo: Manifest.json:

{     "name": "Highlight some phrases",     "description": "Hightlight some pre defined text after page loads",     "version": "0.1",     "permissions": [         "tabs","<all_urls>"     ],     "browser_action": {         "default_icon": "icon.png"     },     "content_scripts": [         {         "matches": [             "http://*/*",             "https://*/*"             ],         "js": ["content.js"],         "run_at": "document_end"    // Pay attention to this line         }     ],      "manifest_version": 2 } 

and content.js:

// alert("hello"); document.body.style.background = 'yellow'; 

Yes, that's enough.
And of course, don't forget to add an icon named icon.png at the same directory with these two files, then test it in Google Chrome.