[Phpmyadmin-devel] AJAX error reporting system (catching errors)

[Rouslan Placella]

On 06/12/2013 07:50 AM, Mohamed Ashraf wrote:
> I was researching about how to catch errors in javascript. I faced a
> problem. due to the way javascript works for a try block to catch an
> error it has to be within the context of execution which means in the
> following code:
> 
> try {
> function f(){
> throw new Error()
> }
> } catch (e) {}
> 
> calling f(); the error will not be caught in the try block.
> essentially what this means is that if we need to catch the errors
> using try and catch blocks we need to wrap the inside of every
> function with a try block. I am not sure how feasible is this idea but
> it I am sure it would reduce code readability.
> 
> The other option is using window.onerror which allows you to hook a
> function that gets executed whenever an uncaught exception occurs.
> This is obviously much simpler and less invasive and has an upside
> that errors in any context anywhere will still be reported to the
> hooked function. But there is a catch. which is that window.onerror
> does not provide a stacktrace because it is executed in a different
> context from the error itself. what it has access to is the line
> number, file name and exception message.
> 
> so my question is which method should I use, the surrounding all
> functions by try blocks or using the window.onerror callback method?
> how important is the stacktrace?

Some of my thoughts are:

* Try/catch has a performance penalty
* We need to be able to easily turn off the error reporting feature
* Some/most function names in the stack trace are going to be useless as
the production js code is minified.
* The line numbers in the file will not be of much help either, I guess,
unless we change the way that the files are minified (like forcing line
breaks every few hundred characters).
* If we do want the stack traces, given that we use jQuery, we could tap
into it and whip up our own traces. For example (completely untested code):

var lastException;
(function ($) {
    var bind = $.fn.bind;
    $.fn.bind = function () {
        try {
            throw new Error;
        } catch (exception) {
            lastException = exception;
        }
        bind.apply({}, arguments);
    };
})(jQuery);

Later, lastException can be accessed from window.onerror. Of course,
we'd have to tap into quite a few functions.

To me it sounds like window.onerror is the winner here.

Bye,
Rouslan

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