Chrome extension: how to trap/handle content-script errors globally?

In a Chrome extension, is there a way to globally trap/handle Javascript errors occurring in a content-script? (e.g. for submission to a Javascript error tracking service like bugsnag)

Ideally, I would setup a global window.onerror handler at the top of the content script. But it's not working properly in Chrome 40: the error is caught, but the information supplied is useless: a message of 'Script error' and no url, lineNumber, column or error object with stack.

I created a test extension to show this busted behaviour for content scripts. Details below. Interesting findings:

Reproducing busted window.onerror for Chrome extension content script.

In a new folder, create manifest.json, content-script.js and background-script.js. Then load into Chrome via Window > Extensions > Load unpacked Extension.

  • To see the busted window.onerror info for a content-script error, reload a webpage and look at the devtools console
manifest.json
{
    "name": "Chrome extension content-script errors test",
    "manifest_version": 2,
    "version": "0.0.1",
    "background": {
      "scripts": [ "background-script.js" ]
    },
    "content_scripts": [{
        "matches": ["<all_urls>"],
        "js": ["content-script.js"]
    }]
}
content-script.js
window.onerror = function (errorMsg, url, lineNumber, column, errorObj) {
    console.log('Caught content script error');
    console.log('errorMsg: ' + errorMsg);
    console.log('url: ' + url);
    console.log('lineNumber: ' + column);
    console.log('column: ' + column);
    console.log('errorObj follows:');
    console.log(errorObj);
    return true;
};

console.log('I am a content script, about to throw an error');
throw new Error('Is this error caught?');
background-script.js
window.onerror = function (errorMsg, url, lineNumber, column, errorObj) {
    console.log('Caught background script error');
    console.log('errorMsg: ' + errorMsg);
    console.log('url: ' + url);
    console.log('lineNumber: ' + column);
    console.log('column: ' + column);
    console.log('errorObj follows:');
    console.log(errorObj);
    return true;
};

//To see nice window.onerror behaviour for background script..
//Uncomment 2 lines below, reload extension, and look at extension console
//console.log('I am a background script, about to throw an error');
//throw new Error('Is this error caught?');

Answers


5 months after asking this question, I'm now pretty convinced there isn't currently an easy way to global trap/handle Javascript errors occurring in a content script. As such,

  • I've created a Chrome bug report: window.onerror should contain useful info for thrown error in extension content script. Feel free to chip in with useful comments.
  • If you need to globally trap content script errors, your best bet is to assume window.onerror is busted for now in content scripts. Instead, wrap all Javascript code in try-catch blocks, which gives you access to useful error information. This is trickier than it sounds, as you have to handle both synchronous code (easy) and asynchronous-callback code (trickier). Take a look at this article for starters, and good luck!

Check out TraceKit, that's what we use at our company to do all front-end error logging. If you combine it with a javascript client library for your favorite logging service you're all set.


I know that I'm a little late for this (just over a year), but still wanted to get a possible answer out there. There are two main ways to do this.

The first method is a subset of the chrome.extension API. chrome.extension.lastError catches errors, and sets the message/summary to the string chrome.extension.lastError.message. Unfortunately, that's pretty much all it can do, you can check it out in the Chrome Developer's documentation.

The second method, using event listeners, is window.addEventListener('error', function(e) { ... });, where the event e taken by the callback stores the stack trace of the error to e.error.stack. This can be used either independently or in conjunction with the first method, and you can read about it here.


See the most complete errors handling by Chrome extension content script in https://github.com/barbushin/javascript-errors-notifier/blob/master/content.js - it's source code of JavaScript Errors Notifier extension.


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