Commonly Asked JavaScript Interview Questions and Answers in 2021

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As a JavaScript developer, your future employer or clients rely on you to maintain the front-end functions of their websites and web applications. These online assets play crucial roles in how well businesses perform, especially in the age of e-commerce. To ensure you are the right fit, entities looking to hire your services ask technical and soft-skill JavaScript interview questions. Knowing how to answer them accurately and confidently can help ensure you get your dream job.

Need some extra motivation? JavaScript developers make an average annual salary of $83,311 and can easily earn six figures at senior levels.

What Are the Responsibilities and Skills of the JavaScript Developer?

Your specific responsibilities can vary across companies and job positions. Generally speaking, the larger the company, the more likely you are to focus on specific tasks. The smaller the company, the more likely you are to become responsible for all of the following:

  • Enhance the performance of the web application.
  • Analyze code to determine reliability, risks and requirements.
  • Build sustainable coding that the website owner can use in the future.
  • Collaborate with other developers to create cohesive designs and functionality.
  • Evaluate the feasibility of front-end designs and make modifications.
  • Troubleshoot and resolve bugs.

To successfully complete these tasks, you need specific skill sets. The bigger the company, the more likely it is to request high levels of experience, a bachelor’s degree or professional certifications. These are the most commonly requested requirements:

  • Bachelor’s degree in engineering, MIS, computer science or a similar field
  • Three or more years of experience working with JavaScript
  • Familiarity with HTML5, CSS3 and other web markup tools

What Are Some Common JavaScript Interview Questions and Answers?

Understanding the role you play in business operations can also help you better answer JavaScript interview questions. Be sure to do research before the interview so you can answer the questions in a way that is relevant to the organization, its industry and the demands of that specific JavaScript role.

What Is JavaScript?

According to Mozilla, JavaScript is a programming language used by developers to add advanced functionalities to web pages. It creates pages that are less static and more interactive. This can increase how attention-grabbing the site is and how user-friendly customers perceive it to be. Companies also use JavaScript to create web-based applications.

What Is the Difference Between Java and JavaScript?

This is one of the most common JavaScript interview questions. When asked, developers often note that Java is an object-oriented programming language. Meanwhile JavaScript is an object-based scripting language. JavaScript only powers browser applications, but Java can extend beyond this. Because of this, while Java can operate as an independent language, JavaScript cannot. It is usually embedded into HTML or serves as part of a web page.

What Are Key Features of JavaScript?

JavaScript is a favorite among developers because of its four main features. These features help to put it ahead of the competition. It easily facilitates network-centric applications. The second noteworthy feature is how well it integrates with Java, which can help expand its overall functionality. Another important feature is that, as a scripting language, it is both cross-platform and open. Finally, developers and web admins love JavaScript because it is lightweight.

What Data Types Are Supported By JavaScript?

In spite of its limitations, JavaScript works well with several different data types. If one of the JavaScript interview questions you are asked is what those data types are, list the following:

  • Undefined
  • Boolean
  • Symbol
  • Number
  • Object
  • Null
  • String

Is JavaScript a Case-Sensitive Language?

Some programming languages are so sensitive that even using the wrong case can change the functionality or make the script unusable. JavaScript is one such language. It requires the consistent use of capitalized letters for any identifier, such as function names, variables and keywords.

What Are the Advantages of JavaScript?

There are many advantages to choosing JavaScript over other options:

  • JavaScript enriches the user experience for website visitors and can create a more engaging experience.
  • Engaging and interactive experiences increase how much time customers spend on a page and reduces website bounce rates.
  • JavaScript reduces the need for visitors to frequently reload the page or move to another page to track the information they enter.
  • JavaScript developers and web admins help reduce bottlenecks in server traffic by validating user input before sending off the page to the receiving server(s).
  • Because JavaScript is so lightweight, it loads more quickly than heavier options that can bog down web pages and their corresponding servers.
  • Because of shorter codes, JavaScript often costs less to create, develop and maintain, compared to alternatives.

What Are the Disadvantages of JavaScript?

No programming or scripting language is perfect. When asked JavaScript interview questions, your employer might acknowledge that the pros do outweigh the cons. Even so, developers must acknowledge and address JavaScript’s limitations to protect the client’s interests.

  • Not all browsers interpret JavaScript the same, so admins need to run any script on multiple browsers to ensure consistency and cohesiveness.
  • JavaScript is viewable to users and can become susceptible to unauthorized changes, which can compromise the security of the website and the confidentiality of data it handles.
  • Debugging JavaScript requires advanced attention to detail, because the browser might not generate an error and HTML editors rarely have effective debugging solutions.
  • To make matters worse, all it takes is one code error to completely destabilize JavaScript and make it appear as if the coded functionality does not exist at all.
  • Some programs require multiple-inheritance characteristics to work well, but JavaScript only supports single inheritance.

How Do JavaScript Developers Create an Object?

To create an object in JavaScript, you can use the object literal. If this is one of the JavaScript interview questions you are asked, here is an example illustrating the way it facilitates the object concept:

var emp = {

name: "Alexis",

age: 31

};

How Do JavaScript Developers Create an Array?

Similar to the object creation method, you use an array literal to make an array in JavaScript. Below is an example of how it works:

var x = [];

var y = [1, 2, 3, 4, 5];

How Do JavaScript Developers Write a Simple Function?

When writing a JavaScript function, you follow a special syntax. Note that functions can include underscores, letters, dollar signs and digits — just like variables can. Failing to follow the specific order could make the code unusable. The specific order is the keyword, then a name, then a parenthesis. This is a generic setup:

function name(parameter1, parameter2, parameter3) {

// code to be executed

}

What Is a “Closure” in the JavaScript Programming Language?

JavaScript developers create a closure every time they create a new function. This allows developers to access the scope of outer functions from inner functions. To accomplish this, developers expose one function after defining it inside another.

This is a generic example of accessing the outer function:

var a = 4;

function myFunction() {

return a * a;

}

This is a generic example of accessing the inner function:

function myFunction() {

var a = 4;

return a * a;

}

Need To Learn More About JavaScript?

When practicing your answers for JavaScript interview questions, it’s important to do as much research as possible. As a developer, it’s also important to keep honing your craft. If you are new to JavaScript or thinking of making a career change, getting the right information is even more important.

We recommend SkillCrush, a free coding camp that is committed to offering equal opportunities to all demographics. Another great source is JavaScript.com. It also offers free lessons and the chance to practice on the website.

How Should Developers Prepare for a JavaScript-Related Job Interview?

When preparing for JavaScript interview questions in the tech field, it’s important to remember it is likely to be more practical than most other job interviews. Employers should ask a few general interview questions, but they then dive directly into practical questions about tech. Many employers also issue a small test immediately, so be prepared to take one. In some cases, you might only need to provide oral answers to scenario-type questions. Because of this, the best way to prepare for a JavaScript interview is to practice.

Why Is Interview Preparation Important?

If you are an experienced JavaScript developer, you might feel the practice is unnecessary for your job hunting success. However, chances are that you generally work on specific parts of JavaScript that your current employer or client(s) ask for. This may cause you to lose practice in some of the niche areas new employers might want to ask questions about. Practice helps to ensure you cover all your bases. Tech is also a very relaxed environment compared to other fields, so preparing keeps you on your toes.

Experienced and talented JavaScript developers can be difficult to find and even harder to entice away from well-paying pet projects. Because of this, employers turn to sites like our’s to help them find the right JavaScript developer for their needs.

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