javascript: how to display script errors in a popup alert?

Yes, that is the correct way.

See the reference here:

http://www.javascriptkit.com/javatutors/error2.shtml

And explanation of how to see more details of the error here:

http://www.javascriptkit.com/javatutors/error3.shtml

Their example:

window.onerror = function(msg, url, linenumber) {
    alert('Error message: '+msg+'\nURL: '+url+'\nLine Number: '+linenumber);
    return true;
}

If you wish to display a LIST of errors in a single pop-up, it's trickier.

Since the errors occue 1 by 1, you need to do the following:

• have window.onerror handler store error details in some array

• Check that array periodically - either via a timer, or on every N'th call of window.onerror handler, or both.

  When the check happens, process entire array, display contents as desired, and empty out an array

Just in case someone would like to use it with jQuery:

$(window).on("error", function(evt) {

    console.log("jQuery error event:", evt);
    var e = evt.originalEvent; // get the javascript event
    console.log("original event:", e);
    if (e.message) { 
        alert("Error:\n\t" + e.message + "\nLine:\n\t" + e.lineno + "\nFile:\n\t" + e.filename);
    } else {
        alert("Error:\n\t" + e.type + "\nElement:\n\t" + (e.srcElement || e.target));
    }
});