change color of element Chrome extension

问题

I have created a simple Jquery script as an chrome extension that are suppose to change the font color of a class.

the script is working fine if I use it directly in the console. but if I run it as an extension It wont trigger when the value is higher than one.

Any suggestion of what could be the problem?

Script.js

 (function(){
         $("#ID-layout-1435216276773-counterValue").each(function() {
                var el = $(this);
                var value = parseFloat(el.text());
                if (value > 1) {
                    el
                        .css("font-weight", "bold")
                        .css("color", "red");

                } else {
                    el.css("font-weight", "normal");
                }
            });   

          })();

Manifest

{
"update_url": "https://clients2.google.com/service/update2/crx",

    "name": "Live",
    "version": "0.3",
    "description": "Live",
    "permissions": [
    "tabs","<all_urls>"
    ],
    "browser_action": {
    "default_icon": "icon.png"
    },
    "icons": { 
                "16": "icon.png",
                "48": "icon.png",
                "128": "icon_128.png" 
            },
    "content_scripts": [
        {
        "matches": [
                "https://www.google.com/analytics/web/?hl=en#dashboard/6I8yfVs_TqSQ_b1tOJYR0Q/a8398197w15972131p74378741/*"
            ],
        "run_at": "document_end" ,
        "js": ["script.js"]     
        }
    ], 
    "manifest_version":2
}

回答1:

You have not actually included jQuery in your content script.

Because content scripts run in isolation from the page, it does not matter whether the page itself has jQuery already included. Your script's context does not have it.

However, your code works from the console, because the code is, by default, executed in the page's context (see that <top frame> selector above the console?), which may have jQuery already. Add to that the fact that Chrome console provides a special version of $ to use in the console, even if there is no jQuery (in which case it's an alias for document.querySelector).

To see what's happening if you execute the code in the extension's context, you need to switch to its context (which is created after you inject something).

You need to add jQuery to your extension's files and inject it before your main script:

"content_scripts": [{
    "matches": [
       ...
    ],
    "run_at": "document_end" ,
    "js": ["jquery.min.js", "script.js"]     
}],

来源：https://stackoverflow.com/questions/31383418/change-color-of-element-chrome-extension