20 most common JQuery interview questions and Answers

JQuery Interview Questions and Answers

JavaScript is the standard language for client-side scripting, and jQuery makes it easier to write JavaScript. You can achieve more with just a few lines of jquery code. It is one of the longest used JavaScript libraries, and there are few new projects that use native JavaScript without jquery. For you as a Java Web Developer, it means you'll find many of the jquery interview questions in a Java Web development interview.

Earlier, most of the time was HTTP, HTML, CSS, and JavaScript, but lately, in addition to JavaScript basics, people want to know if you're familiar with JQuery. The 16 jquery questions are prepared for web developers and can be very handy to correct some key concepts before taking a call or video interview round. If you're new to jQuery, it can also help you understand the basics better and motivate you to find more things.

1. What is $ () in the JQuery library? (The answer is as follows)

The $ () function is a nickname for the jquery () function, which at first glance is weird, and makes the jquery code obscure. Once you get used to it, you'll love the simplicity of it. The $ () function is used to wrap any object into a jquery object, and then you are allowed to invoke several different methods defined on the jquery object. You can even pass a selector string to the $ () function, which returns a JQuery object that contains an array of all matching DOM elements. I have seen this question several times, and although it is very basic, it is often used to differentiate whether a developer understands jQuery.

2. There are 5 <div> elements on the page, how can I use jquery to select them? Answer

Another important jQuery issue is based on selectors. JQuery supports different types of selectors, such as the ID selector, the class selector, and the tag Selector. Given that the question does not mention the ID and class, you can use the tag Selector to select all DIV elements. jquery Code: $ ("div"), which returns a JQuery object that contains all 5 div tags. For more detailed answers, refer to the article linked above.

3. What is the difference between the ID selector and the class selector in JQuery? Answer

If you have used CSS, you may know the difference between the ID selector and the class selector, as does jQuery. The ID selector uses the ID to select elements, such as #element1, while the class selector uses CSS class to select elements. Use the ID selector when you only need to select an element, and if you want to select a group of elements with the same CSS class, use the class selector. During the interview process, you have a great chance of being asked to use the ID selector and the class selector to write the code. The following JQuery code uses the ID selector and the class selector:

12	$(‘#LoginTextBox‘)  // Returns element wrapped as jQuery object with id=‘LoginTextBox‘$(‘.active‘) // Returns all elements with CSS class active.

As you can see, the other difference between the ID selector and the class selector from a syntactic point of view is that the former uses the character "#" and the latter with the character ".". For more detailed analysis and discussion, see the answer link above.

4. How do I use jQuery to hide a picture when I click a button?

This is an event handling issue. jquery provides good support for events such as button clicks. You can use the following code to hide a picture that is located by ID or class. You need to know how to set events for the button and execute the Hide () method, as shown in the code below:

123	$(‘#ButtonToClick‘).click(function(){    $(‘#ImageToHide‘).hide();});

I like the problem because it is very close to actual use and the code is not complicated.

5. $ (document). What is the function of ready ()? Why do you use it?(Answer)

This question is very important and is often asked. The Ready () function is used to execute code when a document enters the ready state. jquery allows you to execute code when the DOM is fully loaded (for example, when the HTML is fully parsed by the DOM tree when the build is complete). The biggest benefit of using the $ (document). Ready () is that it works with all browsers, and jquery helps you solve cross-browser challenges. Users who need further information can click on the answer link to see a detailed discussion.

6. What is the difference between the JavaScript window.onload event and the JQuery ready function? Answer

This question and answer is immediately followed by the previous one. The main difference between the JavaScript window.onload event and the JQuery ready function is that the former waits for the DOM to be created and waits until all external resources, including large pictures, audio, and video, are fully loaded. If loading pictures and media content takes a lot of time, the user will feel that the code defined on the Window.onload event has a noticeable delay when it executes.

On the other hand, the jQuery ready () function simply waits on the DOM tree, without waiting for the image or external resources to load, thus executing faster. Another advantage of using JQuery $ (document) is that you can use it more than once in a Web page, and the browser executes them in the order in which they appear in the HTML page, whereas the onload technique can only be used in a single function. Given this benefit, using the jQuery ready () function is better than using JavaScript window.onload events.

7. How do I find the selected items for all the HTML select tags? (The answer is as follows)

This is one of the more difficult jQuery issues in the interview. This is a basic problem, but don't expect every jQuery beginner to know about it. You can use the following jQuery selector to get all the selected items with Multiple=true <select > tags:

1	$(‘[name=NameOfSelectedTag] :selected‘)

This code uses a combination of the property selector and the: Selected selector, which returns only the selected option. You can modify it as needed, such as using the id attribute instead of the name attribute to get the <select> tag.

8. What is the function of each () in JQuery? How do you use it? (The answer is as follows)

each () function is like a Iterator in Java, which allows you to traverse a collection of elements. You can pass a function to each () method, and the called JQuery object executes the incoming function on each of its elements. Sometimes the question is immediately followed by a question, for example, how to display all the selected items in the Alert box. We can use the selector code above to find all the selected items, and then we print them in the alert box using each () method, with the following code:

123	$(‘[name=NameOfSelectedTag] :selected‘).each(function(selected) {    alert($(selected).text());});

where the text () method returns the textual options.

9. How do you add an HTML element to the DOM tree? (The answer is as follows)

You can add an HTML element to the DOM tree using the JQuery method AppendTo (). This is one of the many methods that JQuery offers to manipulate the DOM. You can add an existing element or a new HTML element to the end of the specified DOM element by using the AppendTo () method.

10. Can you select all hyperlinks within a paragraph using the JQuery code? (the answer is slightly)

This is another question about the jQuery face of the selector. Just like any other problem, just a single line of jQuery code can be done. You can use the following JQuery snippet to select all the hyperlinks (<a> tags) that are nested inside the paragraph (<p> tag) ...

What is the difference between a. $ (this) and the This keyword in jQuery? (The answer is as follows)

This is a tricky problem for many jQuery beginners, but it's a simple question. $ (this) returns a JQuery object, which you can invoke with multiple jquery methods, such as text (), get the value in Val (), and so on. This represents the current element, which is one of the JavaScript keywords that represents the current DOM element in the context. You cannot call the JQuery method on it until it is wrapped by the $ () function, for example $ (this).

12. How do you use jquery to extract attributes for an HTML tag, for example. The href of the link? Answer

The attr () method is used to extract the value of an attribute of any HTML element. You first need to use jquery to select and pick all the links or a specific link, and then you can apply the attr () method to get the value of their href attribute. The following code finds all the links in the page and returns the HREF values:

123	$(‘a‘).each(function(){   alert($(this).attr(‘href‘));});

13. How do you use jquery to set a property value? Answer

One additional follow-up to the previous question is that the attr () method, like other methods in jquery, has more capabilities. If you are calling attr (), take a value for example. attr (name, value), where name is the name of the property, and value is the new value of the property.

What is the difference between the detach () and the Remove () methods in jquery? Answer

Although the detach () and remove () methods are used to remove a DOM element, the main difference between the two is that detach () keeps track of the elements that were removed from the past, so it can be canceled, and the Remove () method maintains a reference to the object that was previously deleted. You can also look at the AppendTo () method used to add elements to the DOM.

15. How do you use jquery to add and remove CSS classes to an element? Answer

By using the two jQuery methods of AddClass () and Removeclass (). Changing the class property of an element dynamically can be very simple, for example. Use the class ". Active" to mark their inactive and active states, and so on.

16. What are the main advantages of using a CDN to load the JQuery library? Answer

This is a slightly more advanced jquery question. Well, in addition to the many benefits of saving server bandwidth and faster download speed, the most important thing is that if the browser has downloaded the same version of JQuery from the same CDN, it will not download it again. So today, many public websites use jquery for user interaction and animation, and if the browser already has a downloadable jquery library, the site has a great opportunity to showcase it.

What is the difference between the Jquery.get () and the Jquery.ajax () methods?

The Ajax () method is more powerful and more configurable, allowing you to specify how long to wait and how to handle errors. The Get () method is a specialized method that only gets some data.

What is the method chain in JQuery? What are the benefits of using a method chain?

The method chain is calling another method on the result returned by one method, which makes the code straightforward and performs better with a single round of lookups for the DOM.

　19. What happens if you return false in a JQuery event handler?

This is typically used to prevent events from bubbling up.

　20. Which method is more efficient: document.getElementById ("MyId") or $ ("#myId")?

First, because it calls the JavaScript engine directly.

JQuery Interview Questions and Answers

JavaScript is the standard language for client-side scripting, and jQuery makes it easier to write JavaScript. You can achieve more with just a few lines of jquery code. It is one of the longest used JavaScript libraries, and there are few new projects that use native JavaScript without jquery. For you as a Java Web Developer, it means you'll find many of the jquery interview questions in a Java Web development interview.

Earlier, most of the time was HTTP, HTML, CSS, and JavaScript, but lately, in addition to JavaScript basics, people want to know if you're familiar with JQuery. The 16 jquery questions are prepared for web developers and can be very handy to correct some key concepts before taking a call or video interview round. If you're new to jQuery, it can also help you understand the basics better and motivate you to find more things.

1. What is $ () in the JQuery library? (The answer is as follows)

The $ () function is a nickname for the jquery () function, which at first glance is weird, and makes the jquery code obscure. Once you get used to it, you'll love the simplicity of it. The $ () function is used to wrap any object into a jquery object, and then you are allowed to invoke several different methods defined on the jquery object. You can even pass a selector string to the $ () function, which returns a JQuery object that contains an array of all matching DOM elements. I have seen this question several times, and although it is very basic, it is often used to differentiate whether a developer understands jQuery.

2. There are 5 <div> elements on the page, how can I use jquery to select them? Answer

Another important jQuery issue is based on selectors. JQuery supports different types of selectors, such as the ID selector, the class selector, and the tag Selector. Given that the question does not mention the ID and class, you can use the tag Selector to select all DIV elements. jquery Code: $ ("div"), which returns a JQuery object that contains all 5 div tags. For more detailed answers, refer to the article linked above.

3. What is the difference between the ID selector and the class selector in JQuery? Answer

If you have used CSS, you may know the difference between the ID selector and the class selector, as does jQuery. The ID selector uses the ID to select elements, such as #element1, while the class selector uses CSS class to select elements. Use the ID selector when you only need to select an element, and if you want to select a group of elements with the same CSS class, use the class selector. During the interview process, you have a great chance of being asked to use the ID selector and the class selector to write the code. The following JQuery code uses the ID selector and the class selector:

12	$(‘#LoginTextBox‘)  // Returns element wrapped as jQuery object with id=‘LoginTextBox‘$(‘.active‘) // Returns all elements with CSS class active.

As you can see, the other difference between the ID selector and the class selector from a syntactic point of view is that the former uses the character "#" and the latter with the character ".". For more detailed analysis and discussion, see the answer link above.

4. How do I use jQuery to hide a picture when I click a button?

This is an event handling issue. jquery provides good support for events such as button clicks. You can use the following code to hide a picture that is located by ID or class. You need to know how to set events for the button and execute the Hide () method, as shown in the code below:

123	$(‘#ButtonToClick‘).click(function(){    $(‘#ImageToHide‘).hide();});

I like the problem because it is very close to actual use and the code is not complicated.

5. $ (document). What is the function of ready ()? Why do you use it?(Answer)

This question is very important and is often asked. The Ready () function is used to execute code when a document enters the ready state. jquery allows you to execute code when the DOM is fully loaded (for example, when the HTML is fully parsed by the DOM tree when the build is complete). The biggest benefit of using the $ (document). Ready () is that it works with all browsers, and jquery helps you solve cross-browser challenges. Users who need further information can click on the answer link to see a detailed discussion.

6. What is the difference between the JavaScript window.onload event and the JQuery ready function? Answer

This question and answer is immediately followed by the previous one. The main difference between the JavaScript window.onload event and the JQuery ready function is that the former waits for the DOM to be created and waits until all external resources, including large pictures, audio, and video, are fully loaded. If loading pictures and media content takes a lot of time, the user will feel that the code defined on the Window.onload event has a noticeable delay when it executes.

On the other hand, the jQuery ready () function simply waits on the DOM tree, without waiting for the image or external resources to load, thus executing faster. Another advantage of using JQuery $ (document) is that you can use it more than once in a Web page, and the browser executes them in the order in which they appear in the HTML page, whereas the onload technique can only be used in a single function. Given this benefit, using the jQuery ready () function is better than using JavaScript window.onload events.

7. How do I find the selected items for all the HTML select tags? (The answer is as follows)

This is one of the more difficult jQuery issues in the interview. This is a basic problem, but don't expect every jQuery beginner to know about it. You can use the following jQuery selector to get all the selected items with Multiple=true <select > tags:

1	$(‘[name=NameOfSelectedTag] :selected‘)

This code uses a combination of the property selector and the: Selected selector, which returns only the selected option. You can modify it as needed, such as using the id attribute instead of the name attribute to get the <select> tag.

8. What is the function of each () in JQuery? How do you use it? (The answer is as follows)

each () function is like a Iterator in Java, which allows you to traverse a collection of elements. You can pass a function to each () method, and the called JQuery object executes the incoming function on each of its elements. Sometimes the question is immediately followed by a question, for example, how to display all the selected items in the Alert box. We can use the selector code above to find all the selected items, and then we print them in the alert box using each () method, with the following code:

123	$(‘[name=NameOfSelectedTag] :selected‘).each(function(selected) {    alert($(selected).text());});

where the text () method returns the textual options.

9. How do you add an HTML element to the DOM tree? (The answer is as follows)

You can add an HTML element to the DOM tree using the JQuery method AppendTo (). This is one of the many methods that JQuery offers to manipulate the DOM. You can add an existing element or a new HTML element to the end of the specified DOM element by using the AppendTo () method.

10. Can you select all hyperlinks within a paragraph using the JQuery code? (the answer is slightly)

This is another question about the jQuery face of the selector. Just like any other problem, just a single line of jQuery code can be done. You can use the following JQuery snippet to select all the hyperlinks (<a> tags) that are nested inside the paragraph (<p> tag) ...

What is the difference between a. $ (this) and the This keyword in jQuery? (The answer is as follows)

This is a tricky problem for many jQuery beginners, but it's a simple question. $ (this) returns a JQuery object, which you can invoke with multiple jquery methods, such as text (), get the value in Val (), and so on. This represents the current element, which is one of the JavaScript keywords that represents the current DOM element in the context. You cannot call the JQuery method on it until it is wrapped by the $ () function, for example $ (this).

12. How do you use jquery to extract attributes for an HTML tag, for example. The href of the link? Answer

The attr () method is used to extract the value of an attribute of any HTML element. You first need to use jquery to select and pick all the links or a specific link, and then you can apply the attr () method to get the value of their href attribute. The following code finds all the links in the page and returns the HREF values:

123	$(‘a‘).each(function(){   alert($(this).attr(‘href‘));});

13. How do you use jquery to set a property value? Answer

One additional follow-up to the previous question is that the attr () method, like other methods in jquery, has more capabilities. If you are calling attr (), take a value for example. attr (name, value), where name is the name of the property, and value is the new value of the property.

What is the difference between the detach () and the Remove () methods in jquery? Answer

Although the detach () and remove () methods are used to remove a DOM element, the main difference between the two is that detach () keeps track of the elements that were removed from the past, so it can be canceled, and the Remove () method maintains a reference to the object that was previously deleted. You can also look at the AppendTo () method used to add elements to the DOM.

15. How do you use jquery to add and remove CSS classes to an element? Answer

By using the two jQuery methods of AddClass () and Removeclass (). Changing the class property of an element dynamically can be very simple, for example. Use the class ". Active" to mark their inactive and active states, and so on.

16. What are the main advantages of using a CDN to load the JQuery library? Answer

This is a slightly more advanced jquery question. Well, in addition to the many benefits of saving server bandwidth and faster download speed, the most important thing is that if the browser has downloaded the same version of JQuery from the same CDN, it will not download it again. So today, many public websites use jquery for user interaction and animation, and if the browser already has a downloadable jquery library, the site has a great opportunity to showcase it.

What is the difference between the Jquery.get () and the Jquery.ajax () methods?

The Ajax () method is more powerful and more configurable, allowing you to specify how long to wait and how to handle errors. The Get () method is a specialized method that only gets some data.

What is the method chain in JQuery? What are the benefits of using a method chain?

The method chain is calling another method on the result returned by one method, which makes the code straightforward and performs better with a single round of lookups for the DOM.

　19. What happens if you return false in a JQuery event handler?

This is typically used to prevent events from bubbling up.

　20. Which method is more efficient: document.getElementById ("MyId") or $ ("#myId")?

First, because it calls the JavaScript engine directly.

20 most common JQuery interview questions and Answers