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Ace Your JavaScript Interview: Top Questions and Answers

“To be prepared is half the victory.“ said Miguel de Cervantes - and he was right. If you want to ace your JavaScript interview, you must establish a good foundation both in theory and practice. You need to have a solid understanding of JavaScript fundamentals, including data types, operators, functions, and control structures.
Daniel Zacharias

Code Power Team

October 4, 2023

56% of developers use JavaScript, which makes it the most popular programming language in the world. It’s the 3rd biggest web technology after HTML and CSS, and it integrates with them perfectly. Together they create beautiful, interactive, and engaging websites.

JavaScript enhances people’s interaction with webpages because it adds dynamic elements to them. Examples of using JavaScript are animated graphics, interactive maps, and Facebook timelines.

If you want to build a career as a JavaScript developer, you won’t go wrong, as it’s among the most demanded skills in 2022.

Acing Javascript Interview

“To be prepared is half the victory.“ said Miguel de Cervantes – and he was right. If you want to ace your JavaScript interview, you must establish a good foundation both in theory and practice. You need to have a solid understanding of JavaScript fundamentals, including data types, operators, functions, and control structures.

Also, take into account whether you’re applying for junior or more advanced developer positions. If you’re applying for more advanced developer positions, you should also understand more complex topics like closures, asynchronous programming, and object-oriented programming.

To help you prepare properly, we found the top questions and answers a hiring manager could ask you in your JavaScript interview.

Top Questions and Answers

Here are some key questions and answers to prepare you for landing your position as a JavaScript developer:

1. What is JavaScript?

JavaScript is a client-side as well as server-side scripting language. Developers use it mainly for enhancing the interaction of a user with the webpage. It is a lightweight, interpreted programming language with object-oriented capabilities that allows you to build web-centric applications.

2. What are some of JavaScript’s key features?

JavaScript key features include:

·       Lightweight, interpreted language

·       Complementary to and integrated with Java

·       Object-oriented

·       Dynamically-typed

·       Platform-independent

3. What are the differences between Java and JavaScript?

Java is a complete programming language, while JavaScript is a coded program that you can import into HTML pages. These two languages aren’t interdependent as they’re designed for different intents. Java is an object-oriented programming (OOPS) or structured programming language (like C++ or C), whereas JavaScript is a client-side scripting language.

4. What are JavaScript data types?

JavaScript data types are:

·       Number

·       String

·       Boolean

·       Object

·       Undefined

·       Null

5. What is the difference between undefined and null in JavaScript?

Undefined means a variable has been declared but hasn’t yet been assigned a value. Null is an assignment value that represents no value or no object.

6. What are the escape characters in JavaScript?

Developers use escape characters to represent certain special characters in a string. Examples of escape characters include \n for a new line and \t for a tab.

7. What does the Logical AND (&&) operator do?

The Logical AND (&&) operator returns true if both operands are true, and false if they’re not.

8. What is the difference between == and === operators?

The == operator compares the values of two operands, while the === operator compares both the values and the types of the operands.

9. What is the difference between let and var in JavaScript?

The let keyword declares variables with block scope, whereas the var keyword declares variables with function scope.

10. What is a closure in JavaScript?

A closure is a function that has access to variables in its outer scope, even after the outer function has returned.

11. What is the difference between synchronous and asynchronous code in JavaScript?

Synchronous code executes in sequence, whereas asynchronous code executes out of order. Asynchronous code prevents blocking the main thread and improves performance.

12. What is the difference between call and apply in JavaScript?

Call and apply invoke a function with a specified this value and arguments. The difference is that call takes arguments as a comma-separated list, whereas apply takes arguments as an array.

13. What is the difference between slice and splice in JavaScript?

Slice extracts a portion of an array. Splice adds or removes elements from an array.

14. What is the difference between let and const in JavaScript?

The let keyword declares variables that can be reassigned, and the const keyword declares variables that can’t.

15. What is the difference between map and forEach in JavaScript?

Both map and forEach iterate over an array. Map returns a new array with the results of calling a provided function on every element in the array, while forEach doesn’t return anything.

16. What is the difference between async and defer attributes in JavaScript?

The async attribute loads a script asynchronously. That means that the script won’t block the rendering of the page. The defer attribute loads a script after the page has finished parsing. In that case, the script won’t block the rendering of the page and will execute in the order in which it appears in the HTML.

17. What is the difference between a callback function and a promise in JavaScript?

A callback function is a function that passes as an argument to another function and executes when the other function has finished executing. A promise is an object that represents a value that may not be available yet, but will resolve at some point in the future. Developers use promises to handle asynchronous operations in JavaScript.

Get ready and build a successful career

As JavaScript is the most popular programming language on Earth, you can be sure you chose the right career path. Building your career as a JavaScript developer, your skills will always be in demand. So get ready, practice, and go get that job you want!

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