Callback functions in JQuery

In this chapter, we'll explore the concept of callback functions in jQuery. Callback functions play a crucial role in asynchronous programming, allowing you to execute code after certain actions or events occur. Understanding callback functions is essential for handling asynchronous tasks effectively and building responsive web applications. From basic syntax to advanced usage, we'll cover everything you need to know about callback functions in jQuery.

Introduction to Callback Functions

What are Callback Functions?

A callback function is a function that is passed as an argument to another function and is executed after the completion of a specific task or event. In jQuery, callback functions are commonly used with asynchronous methods such as animations, AJAX requests, and event handlers.

Why are Callback Functions Important?

Callback functions allow you to perform tasks asynchronously, without blocking the execution of other code. They enable you to handle events, manage responses from asynchronous operations, and execute code based on certain conditions or user interactions.

Basic Usage of Callback Functions

Syntax of Callback Functions

In jQuery, callback functions are typically passed as arguments to other functions. The syntax is as follows:

				
					$(selector).action(function(){
    // Code to be executed after the action completes
});

Example: Using Callback Functions with Animations

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Callback Functions in jQuery</title> <script type="litespeed/javascript" data-src="https://code.jquery.com/jquery-3.6.0.min.js"></script> <script type="litespeed/javascript">$(document).ready(function(){$("#animateButton").click(function(){$("#box").animate({left:"200px"},1000,function(){alert("Animation completed!")})})})</script> <style>#box {
            width: 100px;
            height: 100px;
            background-color: #f0f0f0;
            position: relative;
        }</style></head>
<body>
    <div id="box"></div>
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</html>

Explanation:

  • When the “Animate Box” button is clicked, the #box element moves horizontally to the right over one second.
  • After the animation completes, a callback function is executed, displaying an alert message.

Output:

  • Clicking the “Animate Box” button moves the box to the right, and upon completion of the animation, an alert pops up with the message “Animation completed!”.

Advanced Usage of Callback Functions

Chaining Callback Functions

Callback functions can be chained together to execute multiple tasks sequentially.

				
					$(selector).action1().action2().action3(function(){
    // Code to be executed after all actions complete
});

Error Handling with Callback Functions

Callback functions can handle errors and execute alternative code paths in case of failures.

				
					$(selector).action(function(){
    // Code to be executed on success
}, function(){
    // Code to be executed on error
});

Example 1: Animation Callback

In this example, we’ll use a callback function to execute code after an animation completes.

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Animation Callback Example</title> <script type="litespeed/javascript" data-src="https://code.jquery.com/jquery-3.6.0.min.js"></script> <style>#box {
            width: 100px;
            height: 100px;
            background-color: #f0f0f0;
            position: relative;
        }</style></head>
<body>
    <div id="box"></div>
    <button id="animateButton">Animate Box</button> <script type="litespeed/javascript">$(document).ready(function(){$("#animateButton").click(function(){$("#box").animate({left:"200px"},1000,function(){alert("Animation completed!")})})})</script> <script data-no-optimize="1">!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t="undefined"!=typeof globalThis?globalThis:t||self).LazyLoad=e()}(this,function(){"use strict";function e(){return(e=Object.assign||function(t){for(var e=1;e<arguments.length;e++){var n,a=arguments[e];for(n in a)Object.prototype.hasOwnProperty.call(a,n)&&(t[n]=a[n])}return t}).apply(this,arguments)}function i(t){return e({},it,t)}function o(t,e){var n,a="LazyLoad::Initialized",i=new t(e);try{n=new CustomEvent(a,{detail:{instance:i}})}catch(t){(n=document.createEvent("CustomEvent")).initCustomEvent(a,!1,!1,{instance:i})}window.dispatchEvent(n)}function l(t,e){return t.getAttribute(gt+e)}function c(t){return l(t,bt)}function s(t,e){return function(t,e,n){e=gt+e;null!==n?t.setAttribute(e,n):t.removeAttribute(e)}(t,bt,e)}function r(t){return s(t,null),0}function u(t){return null===c(t)}function d(t){return c(t)===vt}function f(t,e,n,a){t&&(void 0===a?void 0===n?t(e):t(e,n):t(e,n,a))}function _(t,e){nt?t.classList.add(e):t.className+=(t.className?" 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</html>

Explanation:

  • Clicking the “Animate Box” button moves the #box element horizontally to the right over 1 second.
  • After the animation completes, a callback function displays an alert with the message “Animation completed!”.

Output:

  • Upon clicking the “Animate Box” button, the box smoothly moves to the right, and after the animation finishes, an alert pops up with the message “Animation completed!”.

Example 2: AJAX Callback

Let’s use a callback function to handle the response of an AJAX request.

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>AJAX Callback Example</title> <script type="litespeed/javascript" data-src="https://code.jquery.com/jquery-3.6.0.min.js"></script> </head>
<body>
    <button id="getDataButton">Get Data</button>
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d=document.createElement("script");d.addEventListener("load",e),d.addEventListener("error",e),t.getAttributeNames().forEach(e=>{"type"!=e&&d.setAttribute("data-src"==e?"src":e,t.getAttribute(e))});let a=!(d.type="text/javascript");!d.src&&t.textContent&&(d.src=litespeed_inline2src(t.textContent),a=!0),t.after(d),t.remove(),a&&e()}function litespeed_inline2src(t){try{var d=urlCreator.createObjectURL(new Blob([t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1")],{type:"text/javascript"}))}catch(e){d="data:text/javascript;base64,"+btoa(t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1"))}return d}</script></body>
</html>

Explanation:

  • Clicking the “Get Data” button sends an AJAX GET request to retrieve data from a mock API endpoint.
  • Upon receiving a response, the callback function updates the content of the #output element with the title of the retrieved data.

Output:

  • Clicking the “Get Data” button fetches data from the API endpoint and displays the title in the designated output area.

Example 3: Event Handling with Callbacks

In this example, we’ll use callback functions to handle events and execute code based on user interactions.

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
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</html>

Explanation:

  • When the “Click Me” button is clicked, a callback function is triggered, displaying an alert with the message “Button clicked!”.

Output:

  • Clicking the “Click Me” button triggers the callback function, and an alert pops up with the message “Button clicked!”.

Example 4: Handling Asynchronous Tasks with Callbacks

In this example, we’ll simulate an asynchronous task and use a callback function to handle its completion.

				
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<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Asynchronous Task with Callback</title> <script type="litespeed/javascript" data-src="https://code.jquery.com/jquery-3.6.0.min.js"></script> </head>
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</html>

Explanation:

  • Clicking the “Simulate Task” button triggers a function that simulates an asynchronous task (e.g., fetching data, processing data).
  • Upon completion of the task, a callback function is executed, updating the content of the #output element with the task completion message.

Output:

  • Clicking the “Simulate Task” button initiates the asynchronous task simulation, and after 2 seconds, the completion message is displayed in the output area.

Callback functions are a fundamental concept in jQuery and asynchronous programming in general. By mastering the use of callback functions, you can create more responsive and dynamic web applications that handle events, animations, and AJAX requests efficiently. Happy coding !❤️

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