10 jQuery Developer interview questions and answers

One of the best ways to determine an interviewee’s depth of knowledge is to have them describe the features of jQuery in their own words. The respondent should be able to describe how jQuery isn’t a programming language on its own—it’s a client-side JavaScript code which helps with tasks such as event handling and Ajax interactions. The respondent should also know that it is an open source code, created to simplify interactions between HTML/CSS documents and Javascript.

They might also be able to explain common features of jQuery, including event handling, AJAX support, easy DOM manipulation, and cross-browser support.

The interviewee should be able to list a few ways that a jQuery library is used. For example, they should tell you how jQuery is used to create browser-compatible web applications and generally improve an application’s performance. They may also be able to describe the advantages of jQuery, such as that it’s helpful for user interface functions because it allows for fewer lines of code to perform functions. 

A strong respondent will also be able to describe it in technical terms: jQuery code helps simplify interactions between a document object model element (DOM element) and Javascript. It then helps improve the functionality of Javascript, also easing AJAX calls. The interviewee should also be able to tell you that jQuery only works for HTML documents; not XML documents. 

This technical question will test the respondent’s understanding of AJAX, which stands for “asynchronous Javascript and XML”. Along with explaining what an AJAX request is, the interviewee should be able to discuss the following parameters used in the AJAX method:

1. URL: A URL is needed to send a request.
2. Type: This specifies whether it is a Get or Post request.
3. Cache: Determines whether a browser should cache a page
4. Data: Describes which data should be sent to the server.

A jQuery specialist will know that selectors help find the HTML elements in jQuery, which then allows a programmer to work with all elements on a given web page. Common selectors the interviewee should reference include name, ID, class selectors, and attribute selectors, which are used to select elements based on attribute value, also known as attr(). 

The interviewee may also be able to describe the process of chaining, which is used to connect events and functions in a selector. Another similar process is method chaining, which is the chain of methods that are executed in a sequence.

Any jQuery expert will have an arsenal of functions they use for effects when building an application. Look for answers that include some of the following functions:

• fadeOut(): This function turns an element from visible to hidden.
• toggle(): The toggle function checks the visibility of a selected element from hidden to visible.
• fadeToggle(): This function toggles between fadein() and fadeout().
• animate(): The animate function allows for custom animations of CSS properties on a web page. The animation effects may include parameters including speed and callback in the syntax. 

The respondent should be able to tell you that CDN means content distribution network and describes a distributed system of servers in various data centers across the cloud. Servers run at a higher bandwidth in a CDN, allowing faster loading times. Examples of CDNs include Microsoft and Google. 

A jQuery programmer should know that events are user actions on a web page. Handling responses to those events is called event handling. The interviewee should also be able to explain how jQuery provides methods for attaching event handlers to selected elements on a web page.

The interviewee should also be able to describe the meaning of a jQuery object, which contains properties such as length, context, and selector.

There are several jQuery plugins, and this question will show you whether the interviewee has a good handle on various plugins. jQuery connect is a jQuery plugin that connects or binds two functions together. A qualified respondent will be able to explain that the latest version of jQuery connect can be downloaded from jQuery.com. 

A qualified or experienced jQuery coder will likely have used jQuery UI and will be able to describe how it’s used. Ideally, the interviewee will understand that jQuery UI is a set of user interface interactions that are built on top of the jQuery Javascript library. 

This question will show you whether the respondent understands why and how the CSS() is used in jQuery. You’ll need to assess if they can explain how it’s used to get or set style properties for selected elements.