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jQuery Interview Questions and Answers

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jQuery is a JavaScript library written to simplify JavaScript tasks i.e. to create dynamic web pages in an easy manner. It is a light-weight and fast library and can help in performing the JavaScript operations in fewer lines of code.

Most Frequently Asked JQuery Interview Questions

1. What is jQuery?
2. What is the difference between JavaScript and jQuery?
3. How to add styles on elements using jQuery?
4. How to disable the input field in jQuery?
5. How to create animation in jQuery?
6. How to trigger an event in input text while typing in jQuery?
7. How to check whether or not an element is blank using jQuery?
8. Why is the Ajax method preferred in jQuery?
9. What is the difference between ‘before()’ and ‘prepend()’ in jQuery?

Basic jQuery Interview Questions and Answers

1. What is jQuery?

jQuery is a lightweight and fast JavaScript library to simplify JavaScript tasks. The purpose of jQuery is to “Write less, do more”.

2. What is the difference between JavaScript and jQuery?

JavaScript vs jQuery

JavaScript is a programming language used to make the webpages interactive.

Example:

document.getElementById("myElement").style.color = "blue"; 

jQuery is a JavaScript library to simplify these tasks.

Example:

$("#myElement").css("color", "blue"); 

3. What is CDN in jQuery?

CDN stands for Content Delivery Network. It is a system used to improve website speed and performance. It delivers content to users based on their geolocation.
Instead of downloading and hosting jQuery, it is preferred to use CDN for better performance.

For example – Google CDN

src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script>.

4. What are jQuery Selectors?

jQuery Selectors are used to select and manipulate HTML Elements.

Example:

$("#myId"); // Selects an element with the ID 'myId' 
$(".myClass"); // Selects all elements with the class 'myClass' 
$("p"); // Selects all <p> elements

5. What is jquery.min.js?

jquery.min.js is the minified version of the jQuery code. It simply means to remove the unnecessary lines of code like spaces, comments, etc so that the file can load faster.

6. What is the $() function in jQuery?

$() function is used to access and manipulate elements in the DOM.

Example:

$(document).ready(function() {
$("#myElement").text("Hello, World!"); // Selects element with ID 'myElement'
})

7. How to select the first child of an element with jQuery?

:first-child selector is used to select the first child of an element in jQuery:

Example:

$("ul li:first-child").css("color", "red");
// Selects the first <li> of a <ul> and changes text color to blue

8. How to select all sibling elements in jQuery?

.siblings() method is used to select all siblings of an element in jQuery.

Example:

$("#myElement").siblings().css("background-color", "blue");
// Selects all siblings of '#myElement' and sets background color to blue

9. How to select an input element in jQuery?

:input selector is used to select an input element in jQuery.

Example:

$(":input").css("border", "2px solid blue");
// Selects all input elements and adds a blue border

10. How to disable the input field in jQuery?

.prop() method is used to disable the input field of an element in jQuery.

Example:

$("input").prop("disabled", true); // Disables all input elements

11. What are jQuery Events?

jQuery Events

The actions that happen on a web page such as hover, clicks, keypress, or form submissions are jQuery Events.

Example: When a button is clicked, an alert box is displayed.

$(document).ready(function() {
$("#myButton").click(function() {
alert("Button clicked!");
});
});

12. What is the use of $(document).ready() function in jQuery?

$(document).ready() function is used to run the code after the DOM is fully loaded.

$(document).ready(function() {
    alert("DOM is ready!");
});

Intermediate jQuery Interview Questions

13. What is the difference between onload() and document.ready() in jQuery?

onload() waits for the complete page to load including images and external resources while document.ready() doesn’t wait for the complete page to load. It triggers as soon as the DOM is fully loaded.

14. How to add styles on elements using jQuery?

To add styles on elements using jQuery, .css() method is used:

Example:

$("#myElement").css({
"color": "blue",
"font-size": "10px"
}); // Changes text color to blue and font size to 10px

15. How to iterate all list elements with jQuery?

To iterate all the elements of a list in jQuery, .each() function is used:

Example:

$("li").each(function(index) {
console.log(" " + index + ": " + $(this).text());
}); // Logs each <li> element's text

16. How to add a toggle option with jQuery?

toggle option with jQuery

.toggle() method is used to add a toggle option in jQuery:

Example:

$("#myButton").click(function() {
$("#myElement").toggle(); // Toggles visibility of '#myElement'
});

17. How to check whether or not an element is blank using jQuery?

.is(“:empty”) is used to check whether an element is blank or not:

Example:

if ($("#myElement").is(":empty")) {
console.log("Element is empty");
}

18. What is the difference between “this” and “$(this)” in jQuery?

  • this refers to the DOM element itself.
  • $(this) converts the DOM element into a jQuery object, allowing the use of jQuery methods.
$("p").click(function() {
console.log(this); // Logs the DOM element
console.log($(this)); // Logs the jQuery object
});

19. How to trigger an event in input text while typing in jQuery?

In jQuery, the input event can be used to trigger an event while typing.

Example:

$("input").on("input", function() {
console.log($(this).val()); // Logs the input value as you type
});

20. How to create animation in jQuery?

To create an animation in jQuery, .animate() method is used:

Example:

$("#Element").animate({
left: '10px',
opacity: '0.4'
}, 1000); // Animates '#Element' to move 10px to the left and change opacity over 1 second

21. How to add a class to an element with jQuery?

element with jQuery

.addClass() is used to add class to an element in jQuery.

Example:

$("#myElement").addClass("myNewClass");
// Adds the class 'myNewClass' to '#myElement'

22. How to get the width and height of an element in jQuery?

To get the height and width of an element, .height() and .weight() methods are used respectively in jQuery.

Example:

var width = $("#myElement").width();
var height = $("#myElement").height();

23. What is the advantage of method chaining in jQuery?

Method chaining is used to perform multiple operations/ actions on the same element in a single line of code. It ensures that there is no need to select the same selector multiple times.

Example:

$("#myElement").css("color", "blue").slideUp(1000).slideDown(1000);

24. How to load JSON data in jQuery?

$.getJSON() method is used to load JSON data in jQuery.
$.getJSON("data.json", function(data) {
    console.log(data); // Logs the JSON data
});

25. How to perform jQuery AJAX requests?

The .ajax() method is used to perform jQuery AJAX (Asynchronous HTTP requests).

$.ajax({
    url: "https://api.example.com/data",
    method: "GET",
    success: function(data) {
        console.log(data); // Handles success response
    },
    error: function(error) {
        console.log("Error:", error); // Handles error
    }
});

26. Why is the Ajax method preferred in jQuery?

 jQuery Ajax Method

Ajax method is preferred to simplify asynchronous requests and handling responses to improve the user experience.

27. Explain the use of the event.preventDefault() method

The event.preventDefault() method is used to stop the default behavior of the element i.e. if an event is cancelable then it will cancel that event and the related action will not occur.

Example:

$("a").click(function(event) {
    event.preventDefault(); // Prevents the default action of the anchor
});

28. How to read, write, and delete cookies in jQuery?

jQuery Cookie plugin is used to write, read and delete cookies.
// Write a cookie

$.cookie("username", "JD");

// Read a cookie

var username = $.cookie("username");
console.log(username);

// Delete a cookie

$.removeCookie("username");

29. What is jQuery Mobile?

jQuery Mobile is a framework built on jQuery for creating responsive, touch-friendly web applications for mobile devices.

30. What are jQuery Plugins?

jQuery Plugin

jQuery Plugins are the lines of code written in JavaScript to extend the functionality of jQuery. These plugins contain useful methods to perform tasks easily such as form validation, date picker, etc.

// Example: Using a date picker plugin

$("#date").datepicker();

Advanced jQuery Interview Questions and Answers

31. What is the purpose of ‘serialize()’ in jQuery?

The serialize() method in jQuery is used to encode a set of form elements into a serialized string that can be submitted to the server. It collects the form data and converts it into a URL-encoded string, like name=value&name=value format. This format is typically used by AJAX requests to submit form data to the server without reloading the page.

32. What is event stopPropagation()?

The stopPropagation() method in jQuery prevents further propagation of the current event in the bubbling phase. When an event happens on an element, it bubbles up the DOM tree. stopPropagation() stops the bubbling to parent elements. This is useful when an inner element’s click should not trigger the parent’s click handler.

33. How do you delay execution in jQuery?

To delay the execution of code in jQuery, we can use the setTimeout() function. It allows specifying code to execute after a delay of milliseconds. For example, to fade an element in after 2 seconds, we can use:

setTimeout(function(){ $("div").fadeIn(); }, 2000);

This delays the fadeIn animation by 2 seconds before executing.

34. What is the purpose of ‘unbind()’ in jQuery?

The unbind() method in jQuery is used to remove event handlers that were bound using bind(), live(), or on(). When we no longer need an event handler, we use unbind() to remove it. This avoids multiple handlers getting attached to the same events. For example, unbinding a click handler on an element removes the handler and prevents it from executing on future clicks.

35. How do you get the index of an element in a set using jQuery?

To get the index of an element within a jQuery selection set, we can use the index() method. It returns the position of the element relative to its siblings. For example, to get the index of a clicked paragraph, we can do:

$("p").click(function(){
var index = $("p").index(this);
console.log(index);
});

36. What is the role of the ‘data()’ method in jQuery?

The data() method in jQuery allows adding, retrieving, and deleting custom data attached to DOM elements. It is used to store arbitrary data associated with elements without modifying the HTML. This provides a way to include additional information about elements that can be used later.

37. How do you handle mouse events like click and double-click in jQuery?

jQuery provides .click(), .dblclick(), and other methods to easily handle mouse events. To attach a click handler, use .click(function(){ /* code here / }). For double click, use .dblclick(function(){ / code */ }). The function will execute whenever the event occurs. We can identify the clicked/double-clicked element using this keyword.

38. What is the difference between ‘find()’ and ‘filter()’ in jQuery?

The main difference between find() and filter() is that find() searches for descendants of elements in the DOM tree, while filter() filters the current selection set itself. Find() looks inside elements for descendant matches and returns a new set. Filter() looks at each element in the current selection set and returns a new set matching the filter criteria.

39. What is the purpose of the ‘serializeArray()’ method in jQuery?

The serializeArray() method in jQuery is used to serialize form elements into an array of names and values. It collects the form elements data and generates a JSON array, which can be sent to the server via AJAX. This is useful for sending form data to the server without a page refresh.
For example, serializeArray() on a form can stringify the form data into an array like [{“name”:”field1″,”value”:”value1″},..] which can then be sent to the server via AJAX.

40. What is the purpose of the ‘fadeIn()’ function?

The fadeIn() function in jQuery is used to gradually increase the opacity of an element to make it visible with a fading effect. It animates the opacity from 0 to 1 within a given duration to create a smooth fade in transition. This is commonly used to display hidden elements on a page with a nice visual effect.
For example, $(“p”).fadeIn(1000) will make the <p> element fade in from invisible to visible over 1 second.

41. What is the role of the ‘next()’ method in jQuery?

The next() method in jQuery gets the immediately following sibling element of each element in the matched set. It returns a new jQuery object containing the next siblings. This is useful when we need to access or manipulate the element following the current one.

42. What is the difference between ‘before()’ and ‘prepend()’ in jQuery?

The main difference between before() and prepend() is their position in inserting content. The before() method inserts content before the selected elements only, while prepend() inserts content as the first child of each element.

43. What is the purpose of the ‘mouseleave()’ function in jQuery?

The mouseleave() function in jQuery is used to detect when the mouse pointer leaves an element. It attaches an event handler to the element that will run if the mouse leaves the element by moving to an area outside of it. This is useful for things like hiding a tooltip when the mouse exits an element.

For example,
$(“p”).mouseleave(function(){ $(this).hide(); }) would hide any <p> element when the mouse leaves it.

44. How can you change the HTML content of an element in jQuery?

To change HTML content in jQuery, use html(). For example: $(“#element”).html(“<p>New content</p>”);. This method sets the HTML content of an element. It’s an easy way to update what’s inside an element using jQuery.

45. What is event bubbling in jQuery?

Event bubbling is when an event triggered on an inner element is also triggered on outer parent elements. In jQuery, event bubbling occurs from the innermost to the outermost elements. This means if you click a child element, the click event will bubble up and also trigger handlers on parent elements.

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About the Author

Technical Research Analyst - Full Stack Development

Kislay is a Technical Research Analyst and Full Stack Developer with expertise in crafting Mobile applications from inception to deployment. Proficient in Android development, IOS development, HTML, CSS, JavaScript, React, Angular, MySQL, and MongoDB, he’s committed to enhancing user experiences through intuitive websites and advanced mobile applications.