When to Decouple Success Callback Functions from jQuery Ajax Calls?

Decoupling Success Callback Functions from jQuery Ajax Calls

When retrieving data from a server using jQuery ajax, it is common practice to define the success callback function within the .ajax() block. This tightly couples the callback handling with the AJAX call, limiting flexibility and reusability.

To define the success callback outside the .ajax() block, a variable to store the returned data is typically declared. However, a more modern approach using deferred objects is recommended.

Since jQuery 1.5, deferred objects offer a better way to handle asynchronous operations like AJAX calls. Here's how you can achieve this:

function getData() {
    return $.ajax({
        url : 'example.com',
        type: 'GET'
    });
}

function handleData(data /* , textStatus, jqXHR */ ) {
    alert(data);
    //do some stuff
}

getData().done(handleData);

This approach decouples the callback handling from the AJAX call, allowing for multiple callbacks, error handling, and synchronization of asynchronous events with ease.

For instance:

// Timer for demo purposes, resolves itself after 5 seconds
var timer = $.Deferred();
setTimeout(timer.resolve, 5000);

// Get data using AJAX and attach done and error handlers
var ajax = getData().done(handleData).fail(error);

// Wait for both AJAX and timer to finish before continuing
$.when(timer, ajax).done(function() {
    // Both AJAX and 5s timer have finished
});

// Additional callbacks can be added even after AJAX call finishes
ajax.done(function(data) {
    //Do some stuff with data
});

This demonstrates the power of deferred objects, enabling greater control and flexibility over asynchronous operations in jQuery applications.

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