Friday, 6 December 2019

Top 20 JQuery Interview Questions And Answers


Ques: 1. How JQuery and JavaScript are different?

Ans: JQuery simplifies the use of the JavaScript language. JavaScript is a language while JQuery is a library built in the JavaScript language that helps to use the JavaScript language.


Ques: 2. Can JQuery fulfill the need JavaScript?

Ans: JQuery is not a replacement of JavaScript. JQuery is a different library which is written on the top of JavaScript. JQuery is a lightweight JavaScript library that emphasizes interaction between JavaScript and html.


Ques: 3. What are the effects methods used in JQuery?

Ans: JQuery enables us to add effects on a web page. JQuery effects can be categorized into fading, sliding, hiding/showing and animation effects. JQuery provides many methods for effects on a web page. These are the effects methods used in JQuery:
    show() - It displays or shows the selected elements.
    hide() - It hides the matched or selected elements.
    toggle() - It shows or hides the matched elements. In other words, it toggles between the hide() and show() methods.
    fadeIn() - It shows the matched elements by fading it to opaque. In other words, it fades in the selected elements.
    fadeOut() - It shows the matched elements by fading it to transparent. In other words, it fades out the selected elements.


Ques: 4. What is the function of ajaxComplete() as JQuery Ajax event method?

Ans: Whenever an Ajax request completes, JQuery triggers the ajaxComplete event. Any and all handlers that have been registered with the .ajaxComplete() method are executed at this time.


Ques: 5. What is the difference between the ID selector and class selector in JQuery?

Ans: ID selector and class selector are the same as they are in CSS. ID selector uses ID while the 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, you can use the class selector.


Ques: 6. What does dollar sign ($) mean in JQuery?

Ans: Dollar sign is nothing but it's an alias for JQuery. Take a look at below JQuery code.
$(document).ready(function(){
});
over here $ sign can be replace with JQuery keyword.
JQuery(document).ready(function()){
});


Ques: 7. What is the difference between body.onload() and document.ready() function?

Ans: Document.ready() function is different from body.onload() function for 2 reasons:
1. we can have more than one document.ready() function in a page where we can have only one body.onload() function.
2. document.ready() function is called as soon as DOM is loaded where body.onload() function is called when everything gets loaded on the page that includes DOM, images and all associated resources of the page.


Ques: 8. What is JQuery UI?

Ans: JQuery UI is a set of user interface interactions, effects, widgets, and themes built on top of the JQuery JavaScript Library. JQuery UI works well for highly interactive web applications with many controls or for a simple page with a date picker control.


Ques: 9. What is the advantage of hosting a JQuery using a CDN?

Ans: CDN stands for Content Delivery Network or Content Distribution Network. It is a large distributed system of servers deployed in multiple data centres across the internet. It provides the files from servers at a higher bandwidth that leads to faster loading time.

Advantages of using CDN are:
·       The JQuery library download time will be reduced. For example - Users in Europe will hit the CDN in Europe and users in the US will hit the US CDN. As a result, this will reduce the overall page load time.
·       The JQuery library will already be cached in the user’s browser if the user visited another website that references the same JQuery library. In this case, the user need not download the JQuery library.

Ques: 10. What is the difference between find and children methods?

Ans: Both the methods are used to filter the child of the matched elements. Find method is used to find all levels down the DOM tree but children method searches only a single level down the DOM tree.


Ques: 11. What do you understand by JQuery.noConflict?

Ans: 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 $ (Which is the default reference of JQuery) as a function or variable name what JQuery has. And in our development life, we are not at all strict to only JQuery.


Ques: 12. Why there are two different version of JQuery library?

Ans: JQuery library comes in 2 different versions:
1). Production
2). Deployment

The production version is quite useful at development time as JQuery is open source and if you want to change something then you can make those changes in production version.
But the deployment version is small version or compressed version so it is impossible to make changes in it. because it is compressed, so its size is very less than the production version which affects the page load time.

Ques: 13. Which are the popular JQuery CDN? and what is the advantage of using CDN?

Ans: There are 3 popular JQuery CDNs:
1. Google
2. Microsoft
3. JQuery
Advantage of using CDN.
1. It reduces the load from your server.
2. It saves bandwidth. JQuery framework will load faster from these CDN.
3. The most important benefit is it will be cached, if the user has visited any site which is using JQuery framework from any of these CDN.


Ques: 14. How to remove a DOM Element using JQuery?

Ans: Sometimes we get a requirement to delete all child nodes and remove DOM elements using JQuery to make a dynamic web page. In this scenario JQuery provides a couple of methods to remove DOM elements. Here are the options:

    empty()
    remove()
    html()

Ques: 15. What are JQuery Events?

ans: When we design dynamic web pages, we need to apply some events such as Mouse Click, for forms submit the form after a button click, change a color after a click, etc.
So in layman language, events are actions that are used for dynamic web pages. When we perform these actions on an HTML page, we can do whatever we want.

We use some event handlers to perform the action. Some important handlers are bind(), unbind(), blur(), off(), hover(), on(), one(), ready(), trigger() etc.


Ques: 16. What is Grouping?

Ans: When more than one selector shares the same declaration, they may be grouped together via a comma-separated list; this allows you to reduce the size of the CSS (every bit and byte is important) and makes it more readable. The following snippet applies the same background to the first three heading elements.h1, h2, h3 {background: red;}


Ques: 17. What do you mean by Semantic HTML?

Ans: Semantic HTML is a coding style where the tags embody what the text is meant to convey. In Semantic HTML, tags like <b></b> for bold, and <i></i> for italic should not be used, reason being they just represent formatting, and provide no indication of meaning or structure. The semantically correct thing to do is use <strong></strong> and <em></em>. These tags will have the same bold and italic effects, while demonstrating meaning and structure (emphasis in this case).


Ques: 18. What is the difference between eq() and get() methods in JQuery?

Ans: eq() returns the element as a JQuery object. This method constructs a new JQuery object from one element within that set and returns it. That means that you can use JQuery functions on it.

get() return a DOM element. This method retrieves the DOM elements matched by the JQuery object. But as it is a DOM element and it is not a JQuery-wrapped object. So JQuery functions can't be used.


Ques: 19. What is difference between prop and attr?

Ans: attr(): Get the value of an attribute for the first element in the set of matched elements. Whereas,.prop(): (Introduced in JQuery 1.6) Get the value of a property for the first element in the set of matched elements.

Attributes carry additional information about an HTML element and come in name="value" pairs. Where Property is a representation of an attribute in the HTML DOM tree. once the browser parse your HTML code, corresponding DOM node will be created which is an object thus having properties.

attr() gives you the value of element as it was defines in the html on page load. It is always recommended to use prop() to get values of elements which is modified via javascript/JQuery , as it gives you the original value of an element's current state. Find out more here.


Ques: 20. Can we execute/run multiple Ajax request simultaneously in JQuery?

Ans: Yes, it is possible to execute multiple Ajax request simultaneously or in parallel. Instead of waiting for first ajax request to complete and then issue the second request is time consuming. The better approach to speed up things would be to execute multiple ajax request simultaneously.

Using JQuery.when() method which provides a way to execute callback functions based on one or more objects, usually Deferred objects that represent asynchronous events.

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