jQuery Interview Questions

jQuery interview questions

Getting a job in the Information Technology sector has never been easy. If you are reading this article, then you are in the right place to address all your queries and concerns in order to crack an interview in the Information Technology sector The Jquery Interview questions and answers that we provide will subsequently help you in cracking interviews and getting a job with an incredible package.

About jQuery

JQuery or JavaScript Query is a lightweight library of all the cross-browsers. In simple terms, it means that Jquery is designed to make the process of navigation element easier and smoother within a browser. You will be able to add or invoke event handlers on your page that supports HTML and also make it simpler to access all the elements present in your web pages. It assists in enabling the visual effects such as animation factor in your website with the help of client-side events, making it accessible to use Ajax in all the tools.

Best jQuery Interview Questions of 2020

1. What is jQuery?

jQuery is a fast and concise JavaScript Library created by John Resig in 2006 with a nice motto - Write less, do more. jQuery simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is a JavaScript toolkit designed to simplify various tasks by writing less code.

2. What are the core features of jQuery?

Following is the list of important core features supported by jQuery −

  • DOM manipulation − The jQuery made it easy to select DOM elements, traverse them and modifying their content by using cross-browser open source selector engine called Sizzle.

  • Event handling − The jQuery offers an elegant way to capture a wide variety of events, such as a user clicking on a link, without the need to clutter the HTML code itself with event handlers.

  • AJAX Support − The jQuery helps you a lot to develop a responsive and feature-rich site using AJAX technology.

  • Animations − The jQuery comes with plenty of built-in animation effects which you can use in your websites.

  • Lightweight − The jQuery is very lightweight library - about 19KB in size ( Minified and gzipped ).

  • Cross Browser Support − The jQuery has cross-browser support, and works well in IE 6.0+, FF 2.0+, Safari 3.0+, Chrome and Opera 9.0+.

  • Latest Technology − The jQuery supports CSS3 selectors and basic XPath syntax.

3. How will you make sure that DOM is ready using jQuery?

Use $(document).ready() function. Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded.

4. How can you create an Object in JavaScript?

JavaScript supports Object concept very well. You can create an object using the object literal as follows −

var emp = {
   name: "Zara",
   age: 10
};

5. How can you read properties of an Object in JavaScript?

You can write and read properties of an object using the dot notation as follows −

// Getting object properties
emp.name  // ==> Zara
emp.age   // ==> 10

// Setting object properties
emp.name = "Daisy"  // <== Daisy
emp.age  =  20      // <== 20

6. How can you create an Array in JavaScript?

You can define arrays using the array literal as follows −

var x = [];
var y = [1, 2, 3, 4, 5];

7.How to read elements of an array in JavaScript?

An array has a length property that is useful for iteration. We can read elements of an array as follows −

var x = [1, 2, 3, 4, 5];

for (var i = 0; i < x.length; i++) {
   // Do something with x[i]
}

8. What is a named function in JavaScript? How to define a named function?

A named function has a name when it is defined. A named function can be defined using function keyword as follows −

function named(){
   // do some stuff here
}

9. How many types of functions JavaScript supports?

A function in JavaScript can be either named or anonymous.

10. How to define a anonymous function?

An anonymous function can be defined in similar way as a normal function but it would not have any name.

11. Can you assign a anonymous function to a variable?

Yes! An anonymous function can be assigned to a variable.

12. Can you pass a anonymous function as an argument to another function?

Yes! An anonymous function can be passed as an argument to another function.

13. What is arguments object in JavaScript?   

JavaScript variable arguments represents the arguments passed to a function.

14. How can you get the type of arguments passed to a function?

Using typeof operator, we can get the type of arguments passed to a function. For example −

function func(x){
   console.log(typeof x, arguments.length);
}

func();                //==> "undefined", 0
func(1);               //==> "number", 1
func("1", "2", "3");   //==> "string", 3

15. How can you get the total number of arguments passed to a function?

Using arguments.length property, we can get the total number of arguments passed to a function. For example −

function func(x){
   console.log(typeof x, arguments.length);
}

func();                //==> "undefined", 0
func(1);               //==> "number", 1
func("1", "2", "3");   //==> "string", 3

16. How can you get the reference of a caller function inside a function?

The arguments object has a callee property, which refers to the function you're inside of. For example −

function func() {
   return arguments.callee; 
}

func();                // ==> func

It redirects the browser to JSP page error.jsp if any uncaught exception is faces during request handling. It is an error processing page.

17. What is the difference between find and children methods?

Find method is used to find all levels down the DOM tree while children method is used to find single level down the DOM tree.

18. What is a CDN?

CDN stands for Content Delivery Network or Content Distribution Network. It is a large distributed system of servers deployed in multiple data centers across the internet. It provides the files from servers at a higher bandwidth that leads to faster loading time. These are several companies that provide free public CDNs:

  • Google
  • Microsoft
  • Yahoo

19. What is the goal of CDN and what are the advantages of using CDN?

The primary goal of the CDN is to provide content to the end-users with high availability and high performance.

Advantages of using CDN:

  • It reduces the load from the server.
  • It saves bandwidth. jQuery framework is loaded faster from these CDN.
  • If a user regularly visits a site which is using jQuery framework from any of these CDN, it will be cached.

20. How can you use a jQuery library in your project?

You can use a jQuery library in the ASP.Net project from downloading the latest jQuery library from jQuery.com and include the references to the jQuery library file in your HTML/PHP/JSP/Aspx page.

  1. <script src="_scripts/jQuery-1.2.6.js" type="text/javascript"></script>   
  2. <script language="javascript">   
  3. $(document).ready(function() {   
  4. alert('test');   
  5. });   
  6. </script>  

21. What are the selectors in jQuery? How many types of selectors in jQuery?

If you want to work with an element on the web page, first you need to find it. Selectors find the HTML elements in jQuery. There are many types of selectors. Some basic selectors are:

  • Name: It is used to select all elements which match with the given element Name.
  • #ID: It is used to select a single element which matches with the given ID
  • .Class: It is used to select all elements which match with the given Class.
  • Universal (*): It is used to select all elements available in a DOM.
  • Multiple Elements E, F, G: It is used to selects the combined results of all the specified selectors E, F or G.
  • Attribute Selector: It is used to select elements based on its attribute value.

22. Explain pge Directives.

Page Directives inform the JSP Engine about headers and facilities that the page receives from the environment. It is found at the top of all JSP pages. Its syntax is <%@ page attribute=”value”>

23. What is a use of jQuery filter?

: jQuery filter is used to filter the specific values from the object. It filters the result of your original query into specific elements.

24. What are the different types of selectors in jQuery?

There are three types of selectors in jQuery:

  • CSS Selector
  • Custom Selector
  • XPath Selector

25. What is the difference between the ID selector and class selector in jQuery? 

ID selector and class selector are the same as they are in CSS. ID selector uses ID while class selector uses a class to select elements.

You use an ID selector to select just one element. If you want to select a group of elements, having the same CSS class, use class selector.

26. What is the use of serialize() method in JQuery?

The jQuery serialize() method is used to create a text string in standard URL-encoded notation. It serializes the form values so that its serialized values can be used in the URL query string while making an AJAX request.

Syntax:

  1. $(document).ready(function(){    
  2.     $("button").click(function(){    
  3.         $("div").text($("form").serialize());    
  4.     });    
  5. });     

27. What is the use of val() method in JQuery?

The jQuery val() method is used:

  • To get the current value of the first element in the set of matched elements.
  • To set the value of every matched element.

Syntax:

  1. $(document).ready(function(){    
  2.     $("button").click(function(){    
  3.         $("div").text($("form").serialize());    
  4.     });    
  5. });     

28. How to add and remove CSS classes to an element using jQuery?

You can use addclass() jQuery method to add CSS class to an element and removeclass() jQuery method to remove CSS class from an element.

CSS addClass() Example

  1. <!DOCTYPE html>    
  2. <html>    
  3. <head>    
  4.  <title>jQuery Example</title>    
  5. <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js">    
  6.  </script>    
  7.  <script type="text/javascript" language="javascript">    
  8. $(document).ready(function()  
  9. {  
  10. $("#btn").click(function()  
  11. {  
  12.     $("#para").addClass("change");  
  13. });  
  14. });  
  15.  </script>    
  16. <style>  
  17.     .change  
  18.     {  
  19.         color:blue;  
  20.     }  
  21. </style>  
  22.  </head>    
  23. <body>    
  24. <p id="para">This method adds CSS class from an element</p>    
  25. <input type="button" id="btn" value="Click me">   
  26. </body>    
  27. </html>    

29. What is the difference between prop and attr?

attr(): It gets the value of an attribute for the first element in the set of matched element.

prop(): it gets the value of a property for the first element in the set of matched elements. It is introduced in jQuery 1.6.

30. What are the two types of CDNs?

There are two types of CDN:

  • Microsoft: It loads jQuery from AJAX CDN.
  • Google: It loads jQuery from Google libraries API.
Career scopes and salary scale

With the development in the Information Technology sector, the scope in the JQuery sector has increased to a significant extent. To meet the increasing demands in the market, software companies dealing with JQuery hire professionals as well as freshers who have the expertise in handling the queries easily. They look for skilled and talented individuals who possess sufficient knowledge and skills to create queries and execute them in HTML browsers with ease.

If you are willing to build your career in this sector, then try to gain as much knowledge as you can while you are pursuing your engineering or bachelor’s degree regarding JQuery. The pay scale for a software engineer having JQuery Skills will start from 90,000 dollars per annum for a fresher, while the experienced ones get a usual thirty to forty percent hike from the previous salary they withdrew.

Conclusion

In this article, you have to learn about the Jquery Interview questions and the career opportunities present in this particular field. If you want to earn a good amount of money in this sector, try to upskill yourself and the work you do on a regular basis, contributing towards the growth of the organizations you are working for.

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