JQuery error property for error handler - javascript

I'm just playing around for the first time with jQuery's ajax functionality. I wanted to add a function that could handle any errors. So, in one of my client javascript blocks, I added the following line:
<script type="text/javascript">
....
$.ajax({ error: function () { alert('boo'); } })
....
</script>
I expected that this would bind the error handler, so that when an error occurs, it would fire the anonymous function included.
What happens instead though, is that it immediately fires the function on page load, as soon as it parses this line of code.
What am I doing wrong? What is the proper way to bind the ajax error handler?

I'm not sure if I understood your question correctly, let me know if I've misunderstood.
I assume that you are trying to create a generic ajax call error handler? If that's the case, you have got the wrong idea.
Are you are just trying to bind the event handler? In this case, you are executing it.
I would recommend you read and check out the examples on these jQuery API reference docs:
API/1.3/Events
Ajax/jQuery.ajax
Also check out the post link provided by F.Aquino and this SO post: JavaScript Exception Handling.
This is could be helpful too: Handling AJAX Errors With jQuery.

You want to change the global settings. Check jQuery documentation.
$.ajaxSetup({
error: function () { alert('boo'); }
});

Related

Cancel jQuery ajax error in .fail() function

I'm working on a site that has a global Ajax error handler in the main page template, like this:
$(document).ajaxError(function (event, request, settings, thrownError) {
postError(thrownError);
})
This updates the page with information about an error from an Ajax request. I am working on a specific Ajax call where I need errors to be handled differently, it will just silently select a value without doing anything about the error. The function is in a handler for a DevExtreme SelectBox that must return a Promise:
return $.ajax({
// stuff
}).fail(function (request, status, error) {
// set value
});
This does what its supposed to in regards to setting the value, but the Ajax error handler still fires. I've tried setting the error to null in the .fail() function but it still gets posted. Is there a way to disable the ajaxError handler for just this one call?
Seems like you want to prevent bubbling the error up for a particular case. See the following post and I believe this is what you are looking for:
Javascript: How to stop multiple jQuery ajax error handlers?
Hope this helps!

Centralize capturing of errors in JQuery

I have 15 $.ajax calls that are JSONP. I'm using this workaround to prevent javascript exceptions like:
Uncaught TypeError: jQuery878937344363463463_8761219911121421 is not a function
I'm using this code in error callback to prevent it from showing up in console.
window[callbackname] = function() {
window[callbackname] = null;
};
However, I think it's bad if I put that code in all my 15 AJAX calls. In AngularJS, we can intercept errors using $httpProvider.interceptors. This allows us to centralize logging rather than individually.
Does jQuery have a similar feature?
In jQuery, you can use $.ajaxSetup() to set shared options that all of your $.ajax calls will use.
See https://api.jquery.com/jquery.ajaxsetup/

Javascript: Errors arent being displayed on event listeners

I have a problem that is driving me crazy. I have two event listeners that appear to be identical. The are being called with the same scope but at different times. I have been using chromes debugger tool to step through them. The first one will throw an error
TypeError: Object 1 has no method 'get'
But the second example simple stops executing
el.on("change:one", function() {
debugger;
a = 1;
a.get();
});
el.on("change:two", function() {
debugger;
a = 1;
a.get();
});
I understand that simple asking why is this happening probably needs a detailed explanation of all the libraries being used etc, so my question is:
Is it possible to not display errors thrown by javascript, and how would I be able to detect whether something is overriding the error reporting functionality
NOTE: In both examples I have determined that window.onerror is null
Backbone invokes event handlers synchronously and doesn't catch handler exceptions. So if you had code that looked like:
el.trigger('change:one'); // handler will throw exception
el.trigger('change:two'); // won't execute
The change:two event will never get triggered, resulting in your change:two handler never getting invoked.

How to manully trigger an ajaxComplete event

Using Jquery I need to trigger a ajaxComplete event.
At the moment I'm using this code with no success
$.getJSON(assetUrl, function (data) {
...
$.trigger("ajaxComplete");
With Error:
TypeError: 'undefined' is not a function (evaluating '$.trigger("ajaxComplete")')
Any idea what I'm doing wrong? Thanks
The ajaxCompleted event is fired on the DOM, and you will need to call the trigger method on a jQuery wrapper element: $(document).trigger(...), for example.
There is not static function "trigger" on the jQuery object (that's what the error message is telling you), you might use $.event.trigger - though I fear that's internal.
However, you won't need to do it manually; getJSON does trigger the event itself. For aborting a running ajax request, see the abort method of XHR objects.
You can define a global jQuery ajaxComplete (and ajaxError) function that will run on document ready and after every completed ajax request. You can define the ajaxComplete function on the intial page load (or whenever really) like this:
$(function(){
$(document).ajaxComplete(function(){
// on complete code
}).ajaxError(function(){
// on error code
});
});
To call this event handler at any time, just execute the following:
$(document).triggerHandler('ajaxComplete');
If anybody else is looking at this, the correct way to manually trigger ajaxComplete is $(document).trigger('ajaxComplete', [xhr, settings]);
It's probably important to pass the xhr object to the ajaxComplete trigger event, as the event handler might need it.
However, you only need this, if you're not making your requests through jquery, since jquery handles this automatically for you.

JavaScript Error Coding

I am having some issues with my homework assignment. I don't know how to start it or how to do it. I don't need the entire code just what is needed for what is being asked. Please can anyone help me on this. I need it ASAP.
Write a custom error handling JavaScript function called processErrors that handles a custom error by assigning it to the onerror event handler. Include the block of JavaScript statements needed to pass the arguments sent by the JavaScript interpreter into the processErrors function, send an alert message with the agreements, return, and write the event handler that calls the processErrors function.
Please can anyone help me.
function handler (processErrors); { onerror="alert ('There was a custom error')"}
This type of stuff can be a bit challenging when you are completely new to it, so Ill help. In an html page, put something like the following
<script>
function handler(event) {
alert(event);
}
</script>
note that example is not complete according to your question. what this does is declare a js function, 'handler', that takes an argument, 'event', and then pops up the event. This is done is 'script' tags, which you should also expand according to your research.
The next thing you will have to do is assign the function defined above that you complete, to the onerror event of some dom, as shown here: http://www.w3schools.com/jsref/event_onerror.asp
Look here for more guidance on js.
http://www.w3schools.com/js/default.asp
You also might want to google things like: "html script tags" and "javascript event handlers"

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