Top 11 JavaScript Developer Interview Questions for 2022

Hiring developers is often a more painstaking task than the hiring process in other fields. 

This is because software development is a very technical field. And you need to make sure your job candidates are up-to-date on the tools and skills necessary to build your software project. 

When it comes to JavaScript developers, you will want to have a handcrafted set of JavaScript interview questions to truly test your potential hire’s knowledge. 

These 11 JavaScript developer interview questions are a great place to start. Check them out below!

1. Name two principle programming paradigms for JavaScript development. 

JavaScript is a multi-paradigm programming language that supports:

  • Imperative/procedural programming
  • Object-oriented programming (OOP)
  • Functional programming 
  • Prototyped-based programming or prototypical inheritance (an extension of OOP)

Your candidate should be able to name at least two of the above programming paradigms. Although it might be a red flag if there’s no mention of object-oriented programming whatsoever. 

2. Describe the difference between one-way data flow and two-way data binding. 

In unidirectional or one-way data flow, data can only go to one destination. 

For example, a change in the presentation layer or view in a JavaScript program does not change the model or business logic behind the scenes. 

The advantage of this approach is that code is typically easier to debug and there are fewer errors overall. 

On the other hand, in bidirectional or two-way data binding, the data flow can take place in both directions. 

This is what distinguishes Angular vs. React, two prominent JavaScript frameworks. 

Angular’s bidirectional binding means that changes in the model or view of the software architecture ultimately affect one another. 

Two-way data binding can be an effective strategy if you want to share data between a component class and its template. 

3. What are the pros and cons of monolithic versus microservice architecture?

Monolithic vs. Microservice Architecture

Pros of monolithic architecture: 

  • Simplifies cross-cutting concerns where aspects are inevitably intertwined 
  • Performance advantages; monolithic programs are simpler and easier to process in memory

Cons of monolithic architecture:

  • Tight coupling; the interdependency of components complicates scalability and code management 
  • The same tech stack must be used throughout the application 

Pros of microservice architecture:

  • Loose coupling; the lack of dependencies means that code is continuously adaptable
  • Scalability; functions are composed as services so scaling can happen on a component basis rather than holistically 

Cons of microservice architecture:

  • It’s hard to find talented developers who can implement microservices within your software product
  • Testing is more difficult 

4. What is a closure in JavaScript? Provide an example. 

A closure is a function that has access to variables and/references outside of its standard scope. 

function hireDevs() {
  var name = 'Trio';
  function displayName() {
    alert(name);
  }
  return displayName;
}

var myFunc = hireDevs();
myFunc();

In most programming languages, the code here would not run. Traditionally, local variables within a function only exist for the duration of the function’s execution. 

However, print this code in any JavaScript editor and you’ll get a pop-up alert reading “Trio” just the same. 

JavaScript functions form closures using a lexical environment consisting of any local, in-scope variables at the time of the closure’s creation. 

Since a normal function does not have this capacity, it’s imperative that your JavaScript developer knows how to describe and apply this principle in action. 

5. Name and identify the basic data types of JavaScript.

JavaScript has seven basic data types, which should be easy enough for any JavaScript developer worth their salt to remember. 

Most JavaScript developers prepare for the interview process ahead of time, so it’s important that your candidate is well-studied. 

Boolean — returns true or false

Null — represents unknown values, empty, or nothing

Number — used for integers and floating-point (decimal) values

Object — can store data or other complex entities 

String — for any combination of alphanumeric values

Symbol — creates unique identifies for objects

Undefined — value not assigned 

6. Explain the call() method. 

The call() method points to JavaScript’s object-oriented capabilities. It invokes a method by specifying the owner object. 

Essentially, this allows developers to use the method of another object and also use its corresponding arguments. 

This ability relies on the implied JavaScript rule that if a function is not a method of a JavaScript object, it is a function of the global object. 

7. What’s is the use of the NaN() function?

The NaN() function has only one purpose — to check whether a value is an illegal number. 

The program will return a Boolean object of true or false. Applied aptly, the function can mitigate many runtime errors. 

8. What will “console.log(1 < 2 < 3); console.log(3 > 2 > 1);” return?

You probably recognize these logical operators from an elementary math class years ago. However, they don’t quite work the same in JavaScript. 

The first statement returns true but the second returns false. This is because JavaScript reads from left to right, and evaluates expressions one-on-one. 

For the first statement, it is true that one is less than two and two is less than one. Makes sense, right?

In the second statement, three is more than two, so you’re still on the right track. But at this point, JavaScript returns the entire expression as true. 

Now, the comparison is between true and one. Ironically, JavaScript does have a numerical value for true, which is equal to one. 

However, one is definitely not more than one, making the entire statement false. 

9. What does the ‘this’ keyword do?

The this keyword is a self-reference for JavaScript objects. Simply put, it’s a way to refer to the current object within the class definition itself.  

10. Describe the various ways to create an array object in JavaScript.

There are three different ways to create an array in JavaScript. 

  • Create an instance of an array 
    Ex: var exArray = new Array();
  • Use an array constructor
    Ex: var exArray = newArray(“hire”,”Trio”,”developers”);
  • Use an array literal
    Ex: var exArray = [“hire”,”Trio”,”developers”];

11. What is JavaScript?

As a bonus, your JavaScript developer interview questions should include at least one question asking the interviewee to describe JavaScript in layman’s terms. 

Keep this question open-ended, so you can see how much or how little your potential hire knows. 

First and foremost, they should make a point to explain what JavaScript is used for

JavaScript is a front-end programming language. Along with CSS and HTML, it is the backbone of nearly every website’s user interface (UI). 

Thanks to the interactivity JavaScript provides, there are many JavaScript examples demonstrating the language’s capability in web applications, mobile applications, and even games. 

You should expect a JavaScript developer to know this information. You don’t want to work with a developer who doesn’t know the tools they’re working with. 

Conclusion

These JavaScript developer interview questions only break the surface of what an experienced JavaScript developer should know. format 

Don’t be afraid to add a dozen or more questions to really challenge the job applicant. Of course, this is only the technical interview. Next is the coding challenge!

But if you’re feeling overwhelmed by all the resumes, technical interviews, coding challenges, and general frustrations of the hiring process, you’re not alone. 

For many business owners, this is the most difficult part of software development. 

This is why Trio exists. We endeavor to help businesses in need meet their objectives without all the paperwork. 

Find qualified JavaScript developers at Trio today!

 

 

Cordenne Brewster

Content Writer

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A tech enthusiast whose ardor is best expressed through the written word.

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JavaScript is a programming language for developing user interfaces.

A JavaScript developer is a front-end developer who builds user interfaces using JavaScript.