Loading external javascript in google chrome extension

I'm writing a Google Chrome extension which manipulates the current page (basically adds a button).

In my content script, I want to load the Facebook Graph API:

$fbDiv = $(document.createElement('div')).attr('id', 'fb-root');
$fbScript = $(document.createElement('script')).attr('src', 'https://connect.facebook.net/en_US/all.js');
$(body).append($fbDiv);
$(body).append($fbScript);

console.log("fbScript: " + typeof $fbScript.get(0));
console.log("fbScript parent: " + typeof $fbScript.parent().get(0));
console.log("find through body: " + typeof $(body).find($fbScript.get(0)).get(0));

However, the script doesn't seem to added to body. Here's the console log:

fbScript: object
fbScript parent: undefined
find through body: undefined

Any ideas on what I'm doing wrong?

The issue is that the JavaScript inside the content scripts runs in its own sandboxed environment and only has access to other JavaScript that was loaded in one of two ways:

Via the manifest:

{
  "name": "My extension",
  ...
  "content_scripts": [
    {
      "js": ["https://connect.facebook.net/en_US/all.js"]
    }
  ],
  ...
}

Or using Programmatic injection:

/* in background.html */
chrome.browserAction.onClicked.addListener(function(tab) {
    chrome.tabs.executeScript(null,
                       {file:"https://connect.facebook.net/en_US/all.js"});
});

Be sure to update your manifest permissions:

/* in manifest.json */
"permissions": [
    "tabs", "https://connect.facebook.net"
 ],

Appending a script tag will in effect evaluate the JavaScript in the context of the containing page, outside of the JavaScript sandbox that your JavaScript has access to.

Also, since the FB script requires the "fb-root" to be in the DOM, you will probably need to use the programmatic approach so that you can first update the DOM with the element, then pass a message back to the background page to load the Facebook script so it is accessible to the JavaScript that is loaded in the content scripts.

Google Chrome extensions no longer allow injecting external code directly, however you can still download the code with an Ajax call and feed it to the injector as if it was a code block.

chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
    $.get("http://127.0.0.1:8000/static/plugin/somesite.js", function(result) {
        chrome.tabs.executeScript(tabs[0].id, {code: result});
    }, "text");
});

source: https://stackoverflow.com/a/36645710/720665

If you want to load it as content script:

fetch('https://example.com/content.js')
  .then(resp => resp.text())
  .then(eval)
  .catch(console.error)

If you want to load it as background script. Take https://example.com/bg.js for example.

add the remote js script to the background page file, which is named background.html here

<!DOCTYPE html>
<html>
<head>
  <script src="https://example.com/bg.js"></script>
</head>
<body>
<div>Empty content</div>
</body>
</html>

add https://example.com to the content_security_policy of the manifest.json:

"background": {
  "page": "background.html"
},
"content_security_policy": "script-src 'self' https://example.com ; object-src 'self'",

Requirements:

The remote js script must be served via https instead of http.
You should specify a page rather than a scripts array in the background section

Loading external javascript in google chrome extension

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