Does Javascript fire an event for unhandled/uncaught exceptions?

Question

I'm looking to log unhandled javascript exceptions. Is there an event that fires when an exception isn't caught? I'm looking to catch the exceptions before they cause javascript errors in the browser, but I'd rather not run my entire application inside of a try/catch. Any help would be appreciated. Thanks!

Update: tvanfosson pointed out onerror as a possibility. It is not part of a spec and is only available in IE or Gecko based browsers.

For more information - http://books.google.com/books?id=tKszhx-XkzYC&pg=PA386&lpg=PA386&dq=safari+onerror+javascript&source=web&ots=gQaGbpUnjG&sig=iBCtOQs0aH_EAzSbWlGa9v5flyo#PPA387,M1

OnError Support Table - http://www.quirksmode.org/dom/events/error.html

Mozilla's documentation - https://developer.mozilla.org/en/DOM/window.onerror

WebKit Bug Report - https://bugs.webkit.org/show_bug.cgi?id=8519

Answer 1

Try using an onerror handler. Docs from MDN. This will allow you to do something when an error is detected, but probably won't let you continue in a graceful way that a try/catch block would. Be aware that are undoubtedly differences between browsers in how this is handled.

Answer 2

Check out this Fiddle:

http://jsfiddle.net/xYsRA/1/

window.onerror = function (msg, url, line) {
    console.log("Caught[via window.onerror]: '" + msg + "' from " + url + ":" + line);
    return true; // same as preventDefault
};

window.addEventListener('error', function (evt) {
    console.log("Caught[via 'error' event]:  '" + evt.message + "' from " + evt.filename + ":" + evt.lineno);
    console.log(evt); // has srcElement / target / etc
    evt.preventDefault();
});


throw new Error("Hewwo world.  I crash you!!!");

throw new Error("Hewwo world.  I can only crash you once... :(");

Which prints:

Caught[via window.onerror]: 'Uncaught Error: Hewwo world.  I crash you!!!' from http://fiddle.jshell.net/xYsRA/1/show/:32 fiddle.jshell.net:21
Caught[via 'error' event]:  'Uncaught Error: Hewwo world.  I crash you!!!' from http://fiddle.jshell.net/xYsRA/1/show/:32 fiddle.jshell.net:26
ErrorEvent {lineno: 32, filename: "http://fiddle.jshell.net/xYsRA/1/show/", message: "Uncaught Error: Hewwo world.  I crash you!!!", clipboardData: undefined, cancelBubble: false…}
 fiddle.jshell.net:27\

Notes:

• If you remove the "return true" / "evt.preventDefault()" lines, then after the error is logged, it will print on the JS console in the normal way.

• Contrary to statements made above, window.onerror worked in all the browsers I tested. However, the addEventListener method is probably better anyways and provides richer semantics.