I am trying to load (inject) in page a javascript code. The javascript file is local to the extension. the filepath is ‘js/somefile.js’.
const basePath = chrome.runtime.getURL('');
fetch(chrome.runtime.getURL(filePath), { mode: 'same-origin' }) // <-- important
.then((_res) => _res.blob())
.then((_blob) => {
const reader = new FileReader();
reader.addEventListener('loadend', (data) => {
callback(data.currentTarget.result, basePath);
});
reader.readAsText(_blob);
});
const scriptTag = document.createElement('script');
scriptTag.innerHTML = scriptText;
scriptTag.type = 'text/javascript';
const scriptElement = document[injectLocation].appendChild(scriptTag);
if (removeImmediately) document[injectLocation].removeChild(scriptElement);
My web accessible resources are:
"web_accessible_resources": [{
"resources": [
"js/*.js",
],
"matches": ["<all_urls>"]
}],
"content_security_policy": {
"extension_pages": "script-src 'self'; object-src 'self'",
"sandbox": "sandbox allow-scripts; script-src 'self' 'https://apis.google.com/' 'https://www.gstatic.com/' 'https://*.firebaseio.com' 'https://www.googleapis.com' 'https://ajax.googleapis.com'; object-src 'self'"
},
The error that I get is:
Refused to execute inline script because it violates the following Content Security Policy directive: "script-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-Wq/CW2mxkri68TjkuaA0+LnU0capVpyiEuSA5NOVNfU='), or a nonce ('nonce-...') is required to enable inline execution.
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Answer
You can resolve the inline execution error by changing scriptTag.innerHTML = scriptText; to scriptTag.src = chrome.runtime.getURL(filePath);, no need to fetch the script. Manifest v3 seems to only allow injecting static scripts into the page context.
If you want to run dynamically sourced scripts I think this can be achieved by having the static (already trusted) script fetch a remote script then eval it.
UPDATE: example extension, with manifest v3, that injects a script that operates in the page context.
# myscript.js window.variableInMainContext = "hi"
# manifest.json
{
"name": "example",
"version": "1.0",
"description": "example extension",
"manifest_version": 3,
"content_scripts": [
{
"matches": ["https://*/*"],
"run_at": "document_start",
"js": ["inject.js"]
}
],
"web_accessible_resources": [
{
"resources": [ "myscript.js" ],
"matches": [ "https://*/*" ]
}
]
}
# inject.js
const nullthrows = (v) => {
if (v == null) throw new Error("it's a null");
return v;
}
function injectCode(src) {
const script = document.createElement('script');
// This is why it works!
script.src = src;
script.onload = function() {
console.log("script injected");
this.remove();
};
// This script runs before the <head> element is created,
// so we add the script to <html> instead.
nullthrows(document.head || document.documentElement).appendChild(script);
}
injectCode(chrome.runtime.getURL('/myscript.js'));