Chrome Extension Dev: Modifying the DOM using jQuery

Question

OK. So I've read up on content scripting and the like, including several other SO articles that I'll add below, but this still isn't working!

My _manifest.json_:

{
    "name": "name",
    "version": "1.0",
    "description": "desc",
    "browser_action": { "default_icon": "icon.png" },
    "permissions": [ "tabs", "http://*/*" ],
    "background_page": "background.html",
    "content_scripts": [ {
        "all_frames": true,
        "js": [ "content.js" ],
        "matches": [ "http://*/*", "https://*/*" ] 
    } ]
}

My _background.html_:

<!doctype html>
<html>
  <head>
    <title>Background Page</title>    
    <script src="jquery.min.js"></script>    
    <script src="content.js"></script>
  </head>
  <body>
    <script>
        chrome.browserAction.onClicked.addListener(function(tab) 
        {
            chrome.tabs.executeScript(null, {file:"content.js"});
        });
    </script>
  </body>
</html>

My _content.js_:

$('body').prepend('<h1>Testing!</h1>');
$('body').css('background', '#f00 !important');

For now, I'm just trying to modify the background color of the body of a tab. I've added the click listener to run my background.html file, but it doesn't work. I've breakpointed on the script call in the background.html file when debugging and the executeScript event is hit, but my content.js file breakpoint doesn't get hit. I thought having the content.js file under the "content_scripts" in my manifest.json file was enough, but if I remove my background.html file nothing happens.

Can anyone help me modify the content of a tab in any way?! It feels like I'm missing something, because I feel like I'm making this harder than it is. If there is an easier way than what I'm trying to do, I'm open to any suggestions/best practices.

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This helped but as of manifest v2 you can no longer include inline scripts http://stackoverflow.com/questions/17601615/the-chrome-extension-popup-is-not-working-click-events-are-not-handled/17612988#17612988 — Dylan Valade, Oct 19 '13 at 19:39

serg · Accepted Answer · 2011-11-05T03:04:11.097

Background page is kind of like you own mini server - it is a completely isolated page that has nothing to do with pages a user visits. It is used for controlling the rest of extension components as it is always running in background.

Content scripts are pieces of javascript code that are getting injected into actual pages a user visits and can access and modify parent page's DOM.

So to get your extension working you need to remove

<script src="jquery.min.js"></script>    
<script src="content.js"></script>

from background page, and inject jquery as a content script either through manifest:

"content_scripts": [ {
        "all_frames": true,
        "js": [ "jquery.min.js" ],
        "matches": [ "http://*/*", "https://*/*" ] 
} ]

or with chrome.tabs.executeScript:

chrome.browserAction.onClicked.addListener(function(tab) {
    chrome.tabs.executeScript(null, {file:"jquery.min.js"}, function() {
        chrome.tabs.executeScript(null, {file:"content.js"});
    });
});

score 1 · Answer 2 · answered Nov 05 '11 at 03:00

content.js is trying to use jQuery, yet you haven't injected jQuery to the tab along with your content script. The error in the console is "Uncaught ReferenceError: $ is not defined".

There are two options you could use to inject jQuery:

1) Specify in manifest.json to automatically inject jQuery and your content script:

"js": [ "jquery.min.js", "content.js" ],

or,

2) Inject jQuery via background.html:

chrome.tabs.executeScript(null, {file:"jquery.min.js"}, function() {
    chrome.tabs.executeScript(null, {file:"content.js"});
});

Then, pressing your browser action button will work.

Chrome Extension Dev: Modifying the DOM using jQuery

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2 Answers2