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    jQuery Callback

    jQuery Callback Functions

    Line by line, JavaScript statements are held out. However, because a jQuery effect takes some time to complete, the code in the following line may run even though the one before it is still in progress. JQuery offers a callback function for each effect method to stop this from happening.

    A callback function is one that is carried out after the effect has ended. The effect methods accept a callback function as an argument, and callback functions typically serve as the method’s final argument. For instance, the basic syntax for the callback function in the jQueryslideToggle() effect method is as follows:

    $(selector).slideToggle(duration, callback);

    Take a look at the example below where the slideToggle() and alert() statements are placed next to one another. If you use this code, the alert will appear as soon as you press the trigger button, without having to wait for the slide toggle effect to finish.

    Example

    < !DOCTYPE html>
    < html lang="en">
    < head>
    < meta charset="utf-8">
    < title>Example of jQuery Effect Method without Callback Function< /title>
    < scriptsrc="https://code.jquery.com/jquery-3.5.1.min.js">< /script>
    < style>
    p{
    background:yellow;
    font-size: 24px;
    padding:20px;
        }
    < /style>
    < script>
    $(document).ready(function(){
        $("button").click(function(){
            $("p").slideToggle("slow");
    alert("The slide toggle effect has completed.");
        });   
    });
    < /script>
    < /head>
    < body>
    < p>This is paragraph.< /p>
    < button type="button">Click me< /button>
    < /body>
    < /html>
    

    And here is a modified example of the previous one where the alert() statement has been encapsulated inside a callback function for the slideToggle() method. When the slide toggle effect is finished using this code, an alert message will appear.

    Example

    < !DOCTYPE html>
    < html lang="en">
    < head>
    < meta charset="utf-8">
    < title>Example of jQuery Effect Method with Callback Function< /title>
    < scriptsrc="https://code.jquery.com/jquery-3.5.1.min.js">< /script>
    < style>
    p{
    background:yellow;
    font-size: 24px;
    padding:20px;
        }
    < /style>
    < script>
    $(document).ready(function(){
        $("button").click(function(){
            $("p").slideToggle("slow", function(){
    alert("The slide toggle effect has completed.");
            });
        });   
    });
    < /script>
    < /head>
    < body>
    < p>This is paragraph.< /p>
    < button type="button">Click me< /button>
    < /body>
    < /html>
    

    The callback functions for the other jQuery effect methods, such as show(), hide(), fadeIn(), fadeOut(), animate(), etc., can be defined in a similar manner.

    Note:
    When applying the effect method to multiple elements, the callback function is only called once for each element that was chosen, not once for all of them.
    Example

    < !DOCTYPE html>
    < html lang="en">
    < head>
    < meta charset="utf-8">
    < title>Example of jQuery Callback Executed Multiple Times< /title>
    < scriptsrc="https://code.jquery.com/jquery-3.5.1.min.js">< /script>
    < style>
    h1{
    display:none;
    background:red;
    padding:20px;
        }
    p{
    background:yellow;
    font-size: 24px;
    padding:20px;
        }
    < /style>
    < script>
    $(document).ready(function(){
        $("button").click(function(){
            $("h1, p").slideToggle("slow", function(){
    alert("The slide toggle effect has completed.");
            });
        });   
    });
    < /script>
    < /head>
    < body>
    < h1>This is heading< /h1>
    < p>This is paragraph.< /p>
    < button type="button">Click me< /button>
    < /body>
    < /html>		
    

    When the trigger button is pressed, the example code from above will display the same alert message twice, once for each

    and

    element.

    FAQS

    Q1. What is jQuery callback function?

    Line by line, JavaScript instructions are executed. With effects, however, the subsequent line of code can be executed even though the effect is not yet complete. This may lead to mistakes. You can design a callback function to stop this from happening. After the current effect has finished, a callback function is run.

    Q2. What is callback () in JavaScript?

    A function that is passed as an argument to another function is called a callback. A function may call another function using this method. After another component has completed, a callback function may continue to run.

    Q3. Why callback function is used?

    The main objective of a callback is to run code in response to an event. These actions, like typing or mouse clicks, may have been facilitated by the user. You can tell the application to run this code each time a user clicks a key on the keyboard by using a callback.

    Q4. What is difference between callback and normal function?

    The primary difference between a callback function and a regular function is as follows: A callback function is orginally only defined, in contrast to a normal function that is called directly. Once a particular event has taken place, the function is only invoked and carried out.

    Q5. Why are promises better than callbacks?

    In comparison to callbacks and events, they can handle multiple asynchronous operations with ease as well as offer better error handling. In other words, promises are the best option for managing several callbacks concurrently, preventing the undesirable callback hell scenario.

    Q6. Why callback function is asynchronous?

    Functions which are passed to another function that begins running code in the background are known as asynchronous callbacks. The async correctly implemented is typically called to inform and pass data to the callback function that the background task is complete when the background code completes.

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