jQuery Interview Questions

Introduction To jQuery Interview Questions and Answers

jQuery is a JavaScript library which is based on the principle “write less, do more”. It is fast, lightweight and features rich. jQuery comes along with easy-to-use APIs which makes a lot of tasks easier for UI development like HTML document traversal and manipulation, event handling, adding animation effects to a web page that works seamlessly across all the web browsers. jQuery provides selectors that allow traversing the DOM tree of an HTML document’s structure in an efficient manner. Ajax based applications can be build quick and easy with jQuery. There are several inbuilt methods of jQuery, using which we can create animations and effects like sliding, showing or hiding of element etc with a single line of code.

So you have finally found your dream job in jQuery but are wondering how to crack the jQuery interview and what could be the probable 2019 jQuery Interview Questions. Every interview is different and the scope of a job is different too. Keeping this in mind we have designed the most common jQuery Interview Questions and answers to help you get success in your interview.

Below is the most common feature of 2019 jQuery Interview Questions, that can give you a great foundation in the language which is divided into two parts are as follows:

• Part 1 – jQuery Interview Questions (Basic)
• Part 2 – jQuery Interview Questions (Advanced)

Part 1 – jQuery Interview Questions (Basic)

This first part covers basic jQuery Interview Questions and answers

1. Define jQuery with its core features?

Answer:
jQuery is a fast and lightweight JavaScript library. It simplifies a lot of tasks which consume a lot of time and effort with standard JavaScript. It simplifies rapid web development, Ajax interactions, event handling, animations, and HTML document traversing and manipulation. The main core features of jQuery are:

• DOM manipulation- DOM elements can be easily traversed, modified.
• Animations- Lots of built-in animations.
• AJAX- Assist a lot in developing responsive and feature rich site using AJAX.
• Lightweight- About 19kb in size.
• Event handling- Several events can be captured with ease with event handlers.
• Cross-browser support- Works well with IE 6.0+, Safari, Chrome and Opera, Firefox.

2. What are the selectors in jQuery and how many types are there?

Answer:
Selectors are used to finding the HTML elements. A jQuery selector is a function which makes the use of the expression to find out matching elements from a DOM based on any given criteria. Once we select an element, we can perform certain operations on them. Basic selectors are:
1) Name: Selects all elements which match with the given element Name.
2).Class: Selects all elements which match with the given Class.
3) #ID: Selects a single element which matches with the given ID.
4) Universal (*): Selects all elements available in a DOM.
5) Attribute Selector: Select elements based on its attribute value.

Let us move to the next  jQuery Interview Questions

3. What is the basic difference between body?onload() and document.ready() function?

Answer:
Both functions differ with each other.
1) There can be more than one document.ready() function on a single page whereas only one body. onload() function is allowed.
2) document.ready() function is called as soon as DOM is loaded for a page, whereas body.onload() function is called when everything gets loaded on a page including DOM, images, and resources associated with the page.

4. What is the difference between $(this) and ‘this’ in jQuery?

Answer:
This is the common jQuery Interview Questions asked in an interview. Both references the same element but the difference is that “this” is used in a traditional way but when “this” is used with $() then it becomes a jQuery object on which we can use the functions of jQuery.

Example:

$(document).ready(function()
{
$(‘#clickme’).click(function()
{
alert($(this).text());
alert(this.innerText);
});
});
when only “this” keyword is used then we can use the jQuery text() function to get the text of the element, because it is not a jQuery object. Once the “this” keyword is wrapped in $() then we can use the jQuery function text() to get the text of the element.

5. What are the various AJAX functions in jQuery?

Answer:
Ajax call allows the user to exchange data with a server and update parts of a page without reloading the entire page. Some of the functions of AJAX are as follow:
1)$.ajax(): It is considered to be the lowest level and basic of functions. It is used to send requests. This function can be performed without a selector.
2)$.ajaxSetup(): This function is used to define and set the options for various ajax calls.
For example:

$.ajaxSetup({
"type":"POST",
"url":"ajax.php",
"success":function(data)
{
$("#bar")
.css("background","yellow")
.html(data);
}
});

3) Shorthand ajax methods: They comprise of simply the wrapper function that call $.ajax() with certain parameters already set.
4) $.getJSON(): This is a special type of shorthand function which is used to accept the URL to which the requests are sent. Also, optional data and optional callback functions are possible in such functions.

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Part 2 – jQuery Interview Questions (Basic)

This first part covers Advanced jQuery Interview Questions and answers

6. What is JQuery.noConflict?

Answer:
jQuery no-conflict is an option given by jQuery to overcome the conflicts between the different js frameworks or libraries. When we use jQuery no-conflict mode, we are replacing the $ to a new variable and assigning to jQuery some other JavaScript libraries. Also, use the $ as a function or variable name what jQuery has. And in our development life, we are not at all strict to the only jQuery.

jQuery.noConflict();
jQuery(document).ready(function(){
jQuery("div").hide();
});

We can also use your own specific character in the place of $ sign in jQuery.

var $j = jQuery.noConflict();
$j(document).ready(function(){
$j("div").hide();
});

7.What is the use of jQuery .each() function?

Answer:
It is a general function that will loop through a collection. If there are Array-like objects with a length property, they can be iterated with their index position and value. Other objects can be iterated with key-value properties. This function, however, works differently from the $(selector).each() function that works on the DOM element using the selector. But both iterate over a jQuery object.
When we pass the array-like object to .each() function, the callback function can accept two arguments: index of the item, where index is the numerical zero-based index in the array of the current items and item is the value of the current array.

Example:

$("button").click(function(){
$("li").each(function(){
alert($(this).text())
});
});

Let us move to the next  jQuery Interview Questions

8. What are the methods used to provide effects in jQuery?

Answer:
jQuery provides many wonderful effects, we can apply these effects with a simple configuration. The effect may be hiding, showing, toggling, fadeout, fade in, fade to and so on toggle(), Show() and hide() methods. Similarly, we can use other methods as in the following:

• animate( params, [duration, easing, callback] ) This function makes custom animations for your HTML elements.
• fadeIn( speed, [callback] ) This function fades in all the matched elements by adjusting their opacity and firing an optional callback after completion.
• fadeOut( speed, [callback] ) This function is used to fade out all the matched elements by adjusting their opacity to 0, then setting the display to “none” and firing an optional callback after completion.
• fadeTo( speed, opacity, callback ) This function fade the opacity of all the matched elements to a specified opacity and firing an optional callback after completion.
• stop( [clearQueue, goto end ]) This function stops all the currently running animations.

9. Which one is faster, document.getElementByID(‘txtName’) or $(‘#txtName’).?

Answer:
This is the popular jQuery Interview Question asked in a interview. jQuery method to select txtName via “$(‘#txtName’)” will internally makes a call to document.getElementByID(‘txtName’). As jQuery is written on top of JavaScript and it internally uses JavaScript, so JavaScript is always fast.

10.What is the difference between $(‘div’) and $(‘<div/>’) in jQuery?

Answer:
$(‘<div/>’): This creates a new div element. But this is not added to DOM tree unless we don’t append it to any DOM element, whereas $(‘div’) selects all the div element present on the page.

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