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JQuery interview questions

JQuery interview questions

jQuery is a feature-rich, lightweight, and fast JavaScript library, which makes HTML documents, event handling, Ajax, and animation easier with a simple API that works across almost all browsers. These jQuery interview questions will enhance your skills and help you to write in a mainstream JavaScript library, used by major players. The critical purpose of jQuery is to make using JavaScript more convenient on your website. A great combination of extensibility and flexibility, jQuery takes a lot of general tasks that require multiple lines of JavaScript code and wraps them in a manner that you can use with a single line of code.

Development History of jQuery

jQuery was released by John Resig at the BarCamp NYC in January 2006. Currently, it is headed by Timmy Wilson and managed by a team of expert developers.

Latest Version: The most recent version is 3.4.1, which was released on April 10, 2019.

Advantages

  • Easy to learn and intuitive
  • Deals with many cross-browser bugs
  • Clean and simple syntax
  • Open source library
  • Highly extensible

These jQuery interview questions will help you prepare for your upcoming job interview as well and fast-track your career, whether you are a fresher or an experienced Jquery developer.

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Last update: 14 Sep 2019, 51 Questions and Answers

Most Frequently Asked JQuery interview questions And Answers With Examples:

In the standard URL- encoded notation jQuery serialize() is used to create the text strings. It also forms several other controls.
 

$("button").click(function(){
    $("div").text($("form").serialize());
});

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Alert()- it is a pop up that is intended for the user to click the OK button and vanish once you click.

Confirm ()- it is a wider choice and gives 2 options to the user to choose. It is basically like an if-else statement.

Example

                                                    

Display message with alert() and confirm()

alert('Are you sure to delete this item?');
confirm("Are you sure to delete this item?");

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Onclick- it is a mouse event and occurs when the user clicks the left button of the mouse.

Onsubmit- it is a form event and occurs when a user is trying to submit the form. When form validation is used, then this is considered.

Example

                                                    

$("p").click(function(){
     alert("You clicked here");
});

$("form").submit(function(){
    alert("You form submitted");
});

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In order to concatenate two strings in jQuery concatenate the strings using + consternation operator. You have to follow a sequence of codes soon after it. Once it is done, the strings get concatenate. There are some other alternatives as well.

Example

                                                    

var a = 'Best Interview';
var b = 'Question';
var result = a + b;

// output
Best Interview Question

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You can check it in various ways.

if ($('#element').is(':empty')){
   //write your code here
}

OR

if ( $('#element').text().length == 0 ) {
   // length is 0
}

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remove() detach() empty()
through it matched elements can be removed completely from the DOM it is more like with remove function, but it stores the data associated with elements. it removes all the child elements from the data.
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  • $.ajax() - for async request
  • $.ajaxsetup()- to set default value
  • $.ajaxTransport()- for object transmission
  • $.get() - loads data
  • $.ajaxPrefilter()- handle custom solutions
  • $.getJSON() - loads JSON data
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The latest version of jQuery is jQuery3.3

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The text() method return text value inside an HTML element whereas HTML() method returns the entire HTML syntax.

The text() method is used to manipulate the value and the HTML() method is used to manage the HTML object or properties.

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With the help of CSS() method, we can add or remove CSS properties to an HTML element.

Example

                                                    

Syntax
$(selector).css(property);

$("#divID").css("display", "block");

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When a radio button is selected addition check attribute is not added to it. You have to enter "checked".

Example

                                                    

$(document).ready(function(){
    $("input[type='button']").on('click', function(){
       var radioValue = $("input[name='gender']:checked").val();
       if(radioValue){
          alert(radioValue);
       }
    });
});

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You can use window.location="https://www.bestinterviewquestion.com";

You can also use window.location.href = "https://www.bestinterviewquestion.com";

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setTimeout() setInterval()
It runs the code with the timeout. This function executes the JavaScript statement "AFTER" interval. It runs the code in fixed time intervals depending upon the length of their timeout period.
setTimeout(expression, timeout); setInterval(expression, timeout);
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1. Set a cookie

$.cookie("example", "foo"); // Sample 1
$.cookie("example", "foo", { expires: 7 }); // Sample 2
$.cookie("example", "foo", { path: '/admin', expires: 7 }); // Sample 3

2. Get a cookie

alert( $.cookie("example") );

3. Delete the cookie

$.removeCookie("example");

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parent() method refers to top-level elements in given HTML objects, usually selected by jQuery selector. Parent method is used to manipulate changes to be done at the top level of a nested HTML object.

Example: A paragraph which contains a couple of list elements can be a parent. Usually, Parent is used if there is an action based on the child element or if there is any specific need for a parent to be treated differently.

Example

                                                    

$(document).ready(function(){
    $("span").parent().css({"display": "block", "border": "1px solid red"});
});

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ParseInt() is a method in Java that is used to convert the numbers represented as a string. These numbers are an integer type, and through this method, the string gets converted to an integer.
ParseInt() is used to parse the string and returns it to an integer.

syntax

parseInt(string, radix)

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You have to develop the HTML form with adding jQuery. After writing some validation, proceed with the submission.

$("#bestinterviewquestion").submit(); // using jQuery
document.getElementById("bestinterviewquestion").submit(); // using JavaScript

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By including @ and following the email naming standards, email can be validated using jQuery.

Example

                                                    

function validateEmail(sEmail) {
      var filter = /^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
      if (filter.test(sEmail)) {
          return true;
      } else {
          return false;
      }
}

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We can use regex ([0-9]{10})|(\([0-9]{3}\)\s+[0-9]{3}\-[0-9]{4})

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$("#buttonID").click(function(){
    $("YOUR_TAG_OR_CLASS_OR_ID").removeClass("YOUR_CLASS_NAME");
});

 

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jQuery is a javascript library which was created by John Resig in the year 2006.jQuery was designed to make the javascript coding easy to use while creating the website and the applications. jQuery is the free open-source software. It is the most popular and the most used javascript library.

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As like many other JavaScript libraries, jQuery uses $ as a variable name or function All the functionalities available in jQuery is without using $. The JQuery.noConflict method is used to give control of the $ variable back to the library which implemented it. This helps developers to make sure that the $object of libraries doesn’t conflict with jQuery operations.

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CDN stands for Control Delivery Network.CDN is the group of many servers which are located at the many different locations. The job of these servers is to store the copy of the data with them so that they can acknowledge the data request based on which server is nearest to the end user. As a result, the data reaches to the end user very fast and very less affected by the traffic.

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Selectors are the formats used to identify and operate HTML elements. For instance, to select all checkboxes in a web form then we can use [type="checkbox"] selector.

Example

                                                    

<script>

var input = $( "form input:checkbox" )

.wrap( "" )

.parent()

.css({ background: "yellow", border: "3px red solid" });

</script>

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  • jQuery combines good practices of the programming
  • jQuery application is easy
  • jQuery saves the bandwidth of the server
  • jQuery runs on all internet leading browsers like Firefox, Chrome, Microsoft Edge
  • The coder can add plugins as per their requirement.
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DOM is “Document Object Model” which is treemap of all HTML elements in web form loaded by the browser.

We can use The .ready() method provides a way to run a JavaScript code as soon as the page's Document Object Model (DOM) becomes safe to manipulate.

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The .hide() method is used for hiding a particular element.

Example

                                                    

// With the element initially shown, we can hide it slowly:

$( "#clickme" ).click(function() {
   $( "#book" ).hide( "slow", function() {
      alert( "Animation done." );
   });
});

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toggle() is an important type of procedure that is used to toggle between the methods of the hide() and show(). It simply attached multiple functions to toggle for the selected elements. You can consider that it shows the hidden elements and hide the shown elements.

Syntax

$(selector).toggle(function)

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This is used mostly to return a jQuery object in the code. It can also check if an object exists or not.

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AJAX is a descriptor for Asynchronous XML and JavaScript. It is a group of technologies which work together to give dynamic behavior. It means users can enter data on a web form, and without refreshing the entire page, data can be sent to the server or loaded from server to browser. AJAX is used to load google map.

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jQuery effect methods are used to create custom animation effects on websites.

 

For example, few of the effects methods available in jQuery are:

  • animate()
  • delay()
  • clearQueuue()
  • fadeIn()
  • fadeout()
  • dequeue()
  • fadeTo()
  • fadeToggle()
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$(window).load is provided by the browser to show that all assets on the page (like images, videos) are loaded. So if any calculation or user of assets is needed in the code it should happen after $(window).load is done.

$(document).ready is used for DOM object tree loading. This means that we can be sure that DOM object is ready. Note DOM is loaded before page. So if you are trying to execute any code which uses page assets, it may fail.

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In jQuery, the size or size() methods return the number of elements in the object. The .length does the same activity, but faster compared to size method as it’s a property and size is a method with an overhead functional call.

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jQuery is a client scripting language.

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The element selector in jQuery is used to select multiple elements.

Its syntax is $('element1, element2, element 3,....").

The selection elements need to be specified and then with the help of * elements can be selected in any document.

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Developers can use this.title function inside the function to get the attribute of an HTML tag in jQuery. Use the following script:

Example

                                                    

$('a').click(function() {
    var myTitle = $(this).attr ( "title" ); // from jQuery object
    //var myTitle = this.title; //javascript object
    alert(myTitle);
});

 

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jQuery comes with two syntaxes, addClass()and,removeClass() to respectively add or remove CSS classes dynamically.

 

These can be used with the following syntax forms:

  • $(‘#para1’).addClass(‘highlight’);
  • $(‘#para1’).removeClass(‘highlight’);
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The document.getElementbyId( "ourID") is faster because it calls the JavaScript engine directly. jQuery is a wrapper that standardizes DOM control such that it works reliably in each significant browser. A jQuery object is built by the $ sign, and it will first parse the selector as jQuery can search things via attribute, class, etc. The document.getElementbyId can only find the elements by the id.

A jQuery object is actually not a native object so it takes time to create one and it additionally has considerably more potential.

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Using the jQuery attr() method attributes, an element can be set and added. This is also dynamically done in HTML elements.

Example

                                                    

$("#bestinterviewquestion").click(function(){
   $("p").attr("padding","10px");
});

 

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Developers can use the removeAttr() method to remove an attribute of an HTML tag in jQuery. This method can remove one or more attributes from the selected element.

The syntax to use the following action is: $(selector).removeAttr(attribute)

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To achieve the following function, we can use the val() function or attr function (limited to some fields).

The syntaxes to be used to receive the input value of an element using jQuery are as following:

$('#someInput').val();

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The HTML() method is utilized to set content. It overwrites the whole content for the matched elements.

Example

                                                    

$('#IDNAME').html('<p>Best Interview Question</p>');

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The preventDefault() function is used to prevent the default action the browser performs on that event, whereas the stopPropagation() method stops the game from bubbling up to the event chain. The divs click handler never works with stopPropagation(). With preventDefault(), the divs click handler works but browsers default action gets stopped.

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In jQuery, the filter() method is used to create an array filled with all array elements that pass a test provided as a function. The technique doesn’t change the original collection or execute the array elements’ functions without values. Simplified, this method is used to filter out all the items that do not match the selected criteria set by the developers. The standards matches will be returned.

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The live() method works for future matching and existing elements, whereas the bind() method works with the components of the attached event that match or exist the selector at the time of the call.

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The .each() function in jQuery is used by developers to iterate over both arrays and objects seamlessly. Where arrays and array-like objects with a length property are iterated by numeric index, other objects are iterated with their named properties.

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The prop() method is used to change properties for HTML tag as per the DOM tree, whereas attr() changes attributes for HTML tags.

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JavaScript is a scripting language used on browser or server side. jQuery is a library for JavaScript. You can write code in JavaScript without needing jQuery, but you can’t write code in jQuery without JavaScript.

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Both .js and min.js have the same functions. But, min.js is a compressed version of .js with comments and whitespaces stripped out of it to preserve bandwidth.

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$(this) method wrapper around the DOM tree method, whereas ‘this’ is a complete DOM tree method.

$(this) method can be used to call jQuery functions, but ‘this’ calls only the DOM tree functions.

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