jQuery Interview Questions

jQueryinterviewquestionsjQuery, along with HTML5 and CSS3, is the foundation of modern front-end web development. It is the most popular JavaScript framework in the world, found in nearly 65% of the top 10,000 websites globally. Robust, lightweight, and easy to use, jQuery also boasts immense popularity among developers who keep churning out incredible plugins for it.

Jobs that require jQuery experience – chiefly front-end web development – are among the highest paying in the industry. You’ll find your knowledge of jQuery as applicable in a small startup as in a big company.

Below, we will take a look at some questions you may be asked in a jQuery interview. If you find yourself struggling with some of these questions, consider taking a refresher course like this in-depth beginner’s guide to jQuery.

With that out of the way, let’s get started.

Q. What is jQuery?

Simple question, right?

Wrong. You’d be surprised at the number of people who falter at this most basic of questions. I’ve heard people describe jQuery as a ‘language’, a ‘scripting tool’ and even a ‘markup language’.

The right answer, of course, is that jQuery is a JavaScript library that facilitates client-side interactions. It’s just one of the many, many JavaScript libraries out there (here’s one list). The only difference between jQuery and the others is its popularity and community support.

Q. Why should you use jQuery?

“To make web pages better” is the right answer, but your interviewer is probably looking at something more nuanced like a list of key jQuery features and advantages, such as:

  • jQuery simplifies client-side scripting (read: front-end development) without adding to page bloat.

  • jQuery is easy to use; it is possible to include advanced jQuery features without knowing how to code thanks to countless existing plugins.

  • Widespread community support. It is also supported by most major platforms.

  • Free, open-source. jQuery is released under the flexible MIT License.

  • Built-in AJAX capabilities, creating animations, applying CSS and event detection.

  • Supported across virtually all modern browsers.

Q. What are the differences between jQuery and JavaScript?

Another question that pops up in a lot of interviewers thanks to its tricky nature. The correct answer, of course, is a resounding “no!” JavaScript is language; jQuery is a library written in that language. You can say that jQuery is one of many particular instances of the JavaScript language.

Confused by the code? Check out this course on jQuery for beginners to clear away your doubts.

Q. What do you need to start using jQuery?

Simple: a reference to the jQuery library. The best way to do this is to add a link to Google’s jQuery developer library in your <head> or before the </body> tag*. This makes sure that you always have the latest version of the jQuery library, and also helps improve page speed.

*Including references to JavaScript/jQuery in the <head> can reduce page load speed (as it forces the browser to load the JS before loading the actual page elements). For performance purposes, it is better to include the link before </body>.

Q. How many jQuery document.ready() instances can you have on one page?

As many as you like! If performance is not a concern (which will never be in a real world setting), you can have as many document.ready() instances as you like, which are written as follows:

$(document).ready(function()
{
// function here
});

Here, $ is an alias for ‘jquery’. Essentially, the above code reads: “jquery(document).ready(function()”. This is used to reduce the amount of typing one has to do.

Q. How many JavaScript libraries can you use on a page alongside jQuery?

Again, the answer is “unlimited”. There is no upper limit to the number of JavaScript libraries you can use on the same page alongside jQuery, though it’s good practice because it’ll just slow down the page.

Q. How many onload() functions can you have on a webpage?

This question typically follows the earlier question on jQuery document.ready() functions. The answer to this one, however, is “one”. The body onload() function can be called only once all the elements on the page have been loaded, which limits the number of times it can be called to just one.

Q. Which version of jQuery should you use – jquery.js or jquery.min.js? Why?

“.min” refers to the ‘minified’ version of a script or stylesheet. Minification removes all excess whitespace and unnecessary characters from the script and makes it load faster on actual live pages. Thus, the minified version of jQuery – jquery.min.js – is called the ‘deployment’ version. The non-minified jquery.js version, on the other hand, is easier to edit, and thus, is called the ‘production’ version.

You would use the production version while making your web pages, deployment version for live pages.

Q. What are some popular CDNs for jQuery? Why should you use them?

We referred to one CDN (Content Delivery Network) in an earlier question – the Google Developer library. CDNs make file delivery far faster than if the same file was self-hosted on your server. Additionally, most visitors will have a cached copy of the file on their computer (since it is already referred to by other websites), which will further increase speed. Plus, as mentioned before, it ensures that you always have the latest version of jQuery.

Some of the popular jQuery CDNs are:

  • Google developer libraries

  • Microsoft Ajax CDN

  • Max CDN (the official jQuery.com CDN)

  • CDNJS CDN

Q. What are selectors in jQuery?

Selectors are the bread and butter of jQuery. This is how you select HTML elements on a web page. You can refer to specific elements by their ID, their class, their type or their attribute. The hierarchy of different selectors is based on existing CSS selectors.

For example, using $(“h1”) will select all h1 headings on a web page. $(“.hello”), on the other hand, will select all CSS classes labelled “hello”.

You can get a list of jQuery selectors from W3Schools here.

The best way to learn jQuery is by actually using jQuery, as this course on beginner to advanced jQuery projects will show you.

Q. What are jQuery Methods?

The question on selectors naturally leads to the question on methods. Methods are basically triggers for functions. They can be attached to event handlers to carry out some action.

For example, if you want to add some text after a class – say, an alert to a discount following a paragraph – you can use the after() event handler, like this:

$(“.discount”).after(“<p>Huge discounts on selected merchandize!</p>”);

jQuery is relatively easy to program in and should be easy to clear in an interview for any experienced candidate. However, you will rarely be asked jQuery questions in isolation; you will also need to be thorough with front-end development fundamentals, including a knowledge of advanced CSS3, HTML5, JavaScript, etc.

You can brush up your knowledge of jQuery in this course on jQuery UI fundamentals.