detect all JS errors, using JS

Question

I know this has probably been asked before, but I can't find where:

I know you can detect JS errors using extensions in stuff, but is there any way to detect ALL errors using JavaScript and display an alert whenever there is one?

@argo49 i need a way to detect it from the script, not the console — markasoftware, Dec 12 '13 at 03:25
Nope, javascript execution generally halts on errors. You could wrap everything in try / catch, but it would probably be better to not write code with errors in it, or at least just use the console to fix them. — adeneo, Dec 12 '13 at 03:26
@Barmar would that work? Just put ALL script in a try/catch? — markasoftware, Dec 12 '13 at 03:26
It will work for everything except syntax errors, since those are detected before anything runs. — Barmar, Dec 12 '13 at 03:27
@adeneo well this error is only happening on mobile, and my friend is testing it for me and for some reason something isn't working right...so i need this — markasoftware, Dec 12 '13 at 03:27
It won't work for callback functions, though, since they're called outside the dynamic scope of the `try`. — Barmar, Dec 12 '13 at 03:27
Mobile testing is available at BrowserStack. I don't know much about the debugging environment for them, though. — Barmar, Dec 12 '13 at 03:28
See this question: http://stackoverflow.com/q/12664434/362536 I tried a bunch of stuff that didn't work in my situation, but most of those will probably work in yours. — Brad, Dec 12 '13 at 03:29
@Barmer how do you wrap 3rd party scripts which you cannot edit in try/catch ? — Daniel W., Jan 22 '19 at 10:04

score 27 · Accepted Answer · edited May 23 '17 at 10:31

27

In the browser define the window.onerror function. In node attached to the uncaughtException event with process.on().

This should ONLY be used if your need to trap all errors, such as in a spec runner or console.log/ debugging implementation. Otherwise, you will find yourself in a world of hurt trying to track down strange behaviour. Like several have suggested, in normal day to day code a try / catch block is the proper and best way to handle errors/exceptions.

For reference in the former case, see this (about window.error in browsers) and this (about uncaughtException in node). Examples:

Browser

window.onerror = function(error) {
  // do something clever here
  alert(error); // do NOT do this for real!
};

Node.js

process.on('uncaughtException', function(error) {
  // do something clever here
  alert(error); // do NOT do this for real!
});

edited May 23 '17 at 10:31

Community

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answered Dec 12 '13 at 03:39

Sukima

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How do you try / catch script errors from 3rd party scripts, which you cannot edit? – Daniel W. Jan 22 '19 at 10:02
1

If a 3rd party script crashes then there is a bug in *their* script and the 3rd party needs to informed so they can fix it. Maybe consider an alternative script or wrap your interface to their script with your own code that knows how to handle errors. For sync calls into a 3rd party lib wrap the call in a try/catch. For async 3rd party libs wrap the calls in a Promise constructor. – Sukima Jan 23 '19 at 18:30
nice, but alert is not built-in function in nodejs, its an extra package... its better u update it to console.log – Eyni Kave Aug 23 '21 at 22:16

score 0 · Answer 2 · answered Aug 27 '21 at 16:52

For JS in Browser

<!DOCTYPE html>
<html lang="en">
<head>
    <script>
        var lastErr;
        function errHand(e) {
            lastErr = e;
            switch (e.target.nodeName) {
                case 'SCRIPT':
                    alert('script not found: ' + e.srcElement.src);
                    break;
                case 'LINK':
                    alert('css not found: ' + e.srcElement.href);
            }
            return false;
        }
        window.onerror = function (msg, url, lineNo, columnNo, error) {
            alert(msg + ' - ' + url + ' - ' + lineNo + ' - ' + columnNo);
            return false;
        }
    </script>
    <script src="http://22.com/k.js" onerror="errHand(event)"></script>
    <link rel="stylesheet" href="http://22.com/k.css" onerror="errHand(event)" type="text/css" />
</head>
<body>
    <script>
        not_exist_function();
    </script>
</body>
</html>

This works for attached js files trace errors just in same origin host environment
For Request error handeling like Ajax/WebSocket its better use their Bulit-In functions
Console functions override not work for reading auto generated browser error logs at this time with latest browser updates

For NodeJS

process.on('uncaughtException', function (err) {
    console.error('uncaughtException:\n' + err.stack + '\n');
})

Use Both of them in the TOP of your codes

detect all JS errors, using JS

2 Answers2

Browser

Node.js

Linked