When will proper stack traces be provided on window.onError function?

The error object, which would contain a “sanitized” stack trace, is now being passed in as the fifth parameter to onerror in Chrome. You can read about it here: https://code.google.com/p/chromium/issues/detail?id=147127

At the time of this writing it’s in Canary and should be pushed out to the stable Chrome release sometime later this month.
If you’re running Canary you can test it like so:

window.onerror = function (message, file, line, column, errorObj) {
    if(errorObj !== undefined) //so it won't blow up in the rest of the browsers
        console.log('Error: ' + errorObj.stack);
}

You can see as per the spec that they’ve also added the column number which IE 10 has also implemented.

You can also checkout the Mozilla discussion: https://bugzilla.mozilla.org/show_bug.cgi?id=355430