Landing your first JavaScript developer role is an exciting step in your coding journey. To help you shine in your interview, we’ve compiled a list of essential JavaScript coding interview questions and answers specifically tailored for freshers in 2024.

This blog post will equip you with the knowledge to confidently tackle basic, intermediate, and even some bonus problem-solving questions. We’ll also provide tips on how to explain your thought process and write clean, efficient code during the interview.

Ace Your Next JavaScript Interview: Essential Questions You Need to Know (2024)

We’ll break down the questions into three categories:

Basic JavaScript Concepts to Nail:
- Understanding Variables and Data Types (numbers, strings, booleans, etc.)
- Working with Operators (arithmetic, comparison, logical, etc.)
- Loops and Conditionals (for loops, while loops, if/else statements)
- DOM Manipulation Basics (getElementById, getElementsByClassName, querySelectors etc.)

Intermediate JavaScript Challenges You Can Conquer:
- Functions and Scope (local vs. global variables, function parameters)
- Arrays and String Manipulation (methods like push, pop, slice, split, filter , reduce etc.)
- Objects and Key-Value Pairs (accessing and modifying object properties)
- Introduction to Asynchronous JavaScript (concept of promises or callbacks)

Advanced JavaScript Skills to Impress (Optional):
- Error Handling (try/catch blocks)
- Closures (functions that remember their outer scope)
- ES6 Features (const, let, arrow functions, etc.)

Decoding JavaScript Interview Questions: Explained with Examples

For each question category, we’ll delve deeper into specific examples. We’ll show you how to approach the question, explain the concept clearly, and provide code examples with best practices.

Here’s a sneak peek at all the concepts with example codes:

Basic Concepts:

Understanding Variables and Data Types (Code):

JavaScript

Working with Operators (Code):

JavaScript

Loops and Conditionals (Code):

JavaScript

DOM Manipulation Basics (Code):

JavaScript

Intermediate Concepts:

Functions and Scope:

It’s generally recommended to use local variables as much as possible to avoid conflicts and unintended side effects. Imagine two functions with the same variable name – if they’re both local, they won’t interfere with each other.

Functions and Scope (Code):

JavaScript

Arrays and String Manipulation:

Interviewer: Write a function that takes an array of strings and returns a new array with all the strings in uppercase.

JavaScript

Filter and Reduce in Arrays

Interviewer: Write a function that takes an array and use filter return with function and reduce function.

JavaScript

Objects and Key-Value Pairs :

Interviewer: Write a function that takes a person object (with properties like name and age) and returns a greeting string like “Hello, Alice (30 years old)”.

JavaScript

Introduction to Asynchronous JavaScript:

JavaScript is single-threaded by default, meaning it can only execute one task at a time. Asynchronous JavaScript allows us to perform operations (like fetching data from a server) without blocking the main thread. This keeps the user interface responsive while the operation is happening in the background. We can use concepts like callbacks or promises to handle asynchronous operations.

By understanding these intermediate concepts and practicing your coding skills, you’ll be well on your way to conquering JavaScript interview challenges! 👨‍💻

Advanced JavaScript Skills to Impress (Optional):

This section dives into some advanced JavaScript concepts that can showcase your in-depth knowledge during an interview.

Error Handling (try/catch blocks):

Interviewer: Explain how error handling with try/catch blocks works in JavaScript.

Error handling allows us to gracefully manage errors that might occur during program execution. We can use try...catch blocks to wrap code that might throw errors and define a catch block to handle those errors. This prevents the program from crashing and allows us to provide informative messages to the user.

JavaScript

Closures (functions that remember their outer scope):

A closure is a function that has access to the variable environment of its outer function even after the outer function has returned. This allows the inner function to remember and manipulate variables from the outer scope, even when the outer function is no longer executing. Closures can be useful for creating private variables or functions that maintain state.

JavaScript

ES6 Features (const, let, arrow functions, etc.):

ES6 introduced several improvements and new features to JavaScript. Some key examples include:

const and let keywords for block-scoped variable declarations (replacing var for better scoping)
Arrow functions for a concise way to write functions
Template literals for string interpolation with backticks (“)
Classes for object-oriented programming with a more familiar syntax
Destructuring for easier extraction of values from arrays or objects
Spread operator (…) for expanding iterables and copying objects

By understanding and using these ES6 features, you can write cleaner, more efficient, and modern JavaScript code.

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Data Manipulation Shortcuts:

Converting a Float to Integer (Floor Operator):
- Use the unary minus (-) operator before Math.floor() to ensure negative numbers are rounded down to the nearest integer:
JavaScript const floatNum = -5.8; const intNum = -Math.floor(floatNum) // -6 (rounds down for negatives)

Converting a String to a Number (Type Coercion):
- JavaScript will often attempt type coercion when using arithmetic operators with strings. However, be cautious as it can lead to unexpected results:
JavaScript

Checking for NaN (Not a Number):
- Use the isNaN() function to determine if a value is Not a Number:
JavaScript

Chaining Array Methods (Functional Programming Style):
- JavaScript allows chaining multiple array methods (like filter, map, reduce) for concise data processing:
JavaScript

Destructuring Assignment:
- Extract values from arrays or objects in a more readable way:
JavaScript

Other JavaScript Shortcuts:

Ternary Operator (Conditional Expression):
- Write a condensed if-else statement:
JavaScript

Default Function Parameters:
- Set default values for function parameters to avoid errors with missing arguments:
JavaScript

Template Literals (Backticks):
- Create multi-line strings and embed expressions:
JavaScript

Remember, mastering these advanced concepts takes practice. Utilize online resources, experiment with the code examples, and keep building your JavaScript skills to become a confident developer!