How can I intercept ajax responses in jQuery before the event handler?

I'd like to register a global event handler for all AJAX requests, so that I can intercept and handle responses from the server before the specific event handler gets them.

For example, my code might have something like:

$("#placeholder").load("/fragments/userpics");

And I'd like to register a "before" event handler so that I could, for example, display a login box if a 401 response is retur开发者_StackOverflowned, or maybe retry if there's a 503 response.

I thought that $.ajaxError() is where I would do something like this, but apparently it is only triggered after the event handler.

UPDATE: OK, here's what I got so far, with the help of @genesis:

$.ajaxPrefilter(function(options, originalOptions, jqXHR) {
    var success = options.success;
    options.success = function(data, textStatus, jqXHR) {
        // override success handling
        if(typeof(success) === "function") return success(data, textStatus, jqXHR);
    };
    var error = options.error;
    options.error = function(jqXHR, textStatus, errorThrown) {
        // override error handling
        if(typeof(error) === "function") return error(jqXHR, textStatus, errorThrown);
    };
});

After doing some testing, it looks like I would also need to override options.complete.

However, this still doesn't cover all the bases, since you can also attach events directly to the jqXHR object, and changing options won't help in this case.

Any tips?

If you want to handle the data coming back from the server before the event handler, use datafilter:

    jQuery.ajaxSetup({
        dataFilter: function (data, type) {
            //modify the data

            return data;
        }
    });

Handle custom Ajax options or modify existing options before each request is sent and before they are processed by $.ajax().

http://api.jquery.com/jQuery.ajaxPrefilter/

I bet it works for .load(), too

Hugo Forte has the correct answer, the only way to intercept an Ajax response before any event handlers are called is to use dataFilter.

I had to use this today to handle redirecting ajax responses on the client side without refactoring the code too much.

$.ajaxSetup({
    dataFilter: function (data, type) {
        if (data !== "" && data === "NOAUTH") {
            window.location = '/';
        }
        return data;
    }
});