handle an exception within the initializer of its object

I'm currently working with an Ajax object that is utilized in various other objects to load 'Json' files.

One issue I'm facing is trying to catch the 404 'Not found' exception thrown in the initializer object. However, every attempt results in:

Uncaught Exception : *********

Here is a snippet of the code in question:

_ajax_params.xmlhttp.onreadystatechange = function() {
    if (_ajax_params.xmlhttp.readyState==4 && _ajax_params.xmlhttp.status==200) {
        _ajax_params.response = _ajax_params.xmlhttp.responseText;
        if (typeof afterClosure == 'function') {
            afterClosure(_ajax_params.response);
        }
        COMMON.always(_ajax_params.response);
    } else if (_ajax_params.xmlhttp.status == 404) {
        throw 'File not found';
    }
};

Within the initializer object:

try {
   Base.include.json(url, 1);
} catch (e) {
   console.error(e);
   Base.include.json(url,2);
}

Despite attempting to re-throw the exception, I keep encountering the same issue.

Answer №1

The callback you've defined may be encapsulated within a try-catch block, but keep in mind that it gets executed outside of this block when the event is triggered. Consequently, any exceptions thrown within the callback won't be caught by the surrounding block.

If you're interested in seeing how this works in practice, check out this demonstration.

Instead of using throw 'File not found';, consider invoking Base.include.json(url,2).

Additionally, it's advisable to only check the status if you're certain that the readyState is at 4; however, this is more of a minor detail.

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