7 Essential JavaScript Interview Questions for Beginners (With Solutions & Explanations)

JavaScript is one of the most in-demand programming languages today. Whether you're preparing for your first job interview or brushing up on your fundamentals, mastering the basics is essential.

In this article, I've compiled 10 beginner-level JavaScript interview questions, complete with solutions and explanations, to help you build confidence and deepen your understanding.

Let’s dive in! 👇

Question 1: What are the different ways to declare variables in JavaScript?
☑️Solution:

var name = "Alice";  // function-scoped
let age = 25;        // block-scoped
const country = "USA"; // block-scoped, constant

💡 Explanation:

• var is function-scoped and allows redeclaration.

• let is block-scoped and allows reassignment but not redeclaration.

• const is block-scoped and does not allow reassignment or redeclaration.

Question 2: What is the difference between == and ===?
☑️Solution:

'5' == 5    // true (loose equality)
'5' === 5   // false (strict equality)

💡 Explanation:

• == checks for value only and performs type coercion.

• === checks for both value and type, making it more reliable.

Question 3: What are the primitive data types in JavaScript?
☑️Solution:

let str = "Hello";      // String
let num = 42;           // Number
let isOnline = true;    // Boolean
let nothing = null;     // Null
let notDefined;         // Undefined
let id = Symbol('id');  // Symbol
let bigInt = 9007199254740991n; // BigInt

💡 Explanation:
JavaScript has 7 primitive types: String, Number, Boolean, null, undefined, Symbol, and BigInt. These are immutable and stored by value.

Question 4: How do you check the type of a variable?
☑️Solution:

typeof "hello";  // "string"
typeof 42;       // "number"
typeof null;     // "object" (quirky behavior!)

Question 5: What is the DOM?
☑️Solution:

document.getElementById("app").innerText = "Hello World!";

The DOM (Document Object Model) is a way JavaScript can interact with HTML and CSS.

Question 6: What’s the difference between var, let, and const?
☑️Solution:

(https://dev-to-uploads.s3.amazonaws.com/uploads/articles/h00m833c53b7a3kxt0rg.png)

Question 7: How does JavaScript compare different types?
☑️Solution:

'5' == 5          // true
'5' === 5         // false
null == undefined // true
null === undefined // false