🟢 Part 7: Top 30 JavaScript Interview Questions for Beginners – Explained with Real-Life Examples

📌 Meta Description:
A must-read for frontend beginners! These 30 JavaScript interview questions come with clear explanations, examples, and comparison tables where needed — making it easy to understand and remember.

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✅ Introduction:

JavaScript is one of the most important languages for frontend development. If you're preparing for your first job as a frontend developer, understanding the core JavaScript concepts is a must.

In this article, we've covered 30 beginner-level JavaScript interview questions. Each answer is written in simple English, with relatable real-world examples, so even if you're hearing the topic for the first time, you'll understand it right away.

Let’s begin!

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🔶 JavaScript Interview Questions and Answers for Beginners:

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1. What is JavaScript?

Answer:
JavaScript is a programming language used to add interactivity to websites. While HTML gives structure and CSS gives style, JavaScript makes your webpage do something — like showing alerts, validating forms, or changing content dynamically.

Example:
When you click a button and a popup appears — that's JavaScript.

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2. Is JavaScript a compiled or interpreted language?

Answer:
JavaScript is an interpreted language. This means code is executed line by line in the browser.

You don’t need to compile JavaScript before running it — the browser reads and runs it directly.

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3. What is the difference between JavaScript and Java?

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4. What are variables in JavaScript?

Answer:
Variables are used to store data. Think of a variable as a container where you keep values like numbers, text, etc.

let name = "Payal";

Here, name is a variable holding the string "Payal".

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5. Difference between var, let, and const?

Real-Life Tip: Use const when the value shouldn't change. Use let for changeable values. Avoid var in modern code.

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6. What is the difference between == and ===?

Answer:

• == compares values (ignores data type).

• === compares values and types.

5 == "5"   // true
5 === "5"  // false

Always prefer === for accurate comparison.

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7. What are data types in JavaScript?

Answer:
JavaScript has 8 basic data types:

• Number (123, 4.5)

• String ("hello")

• Boolean (true/false)

• Null (intentional absence)

• Undefined (no value assigned)

• Object (complex data)

• Symbol (unique identifiers)

• BigInt (very large numbers)

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8. How do you declare an array in JavaScript?

let fruits = ["Apple", "Banana", "Mango"];

An array is a collection of items stored in a single variable.

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9. What is a function in JavaScript?

Answer:
A function is a block of code that performs a task when called.

function greet() {
  console.log("Hello!");
}
greet(); // Output: Hello!

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10. What is the difference between function declaration and function expression?

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11. What is an arrow function?

Answer:
It’s a shorter way to write functions.

const greet = () => console.log("Hi!");

Arrow functions are commonly used in React and modern JS.

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12. What is the difference between null and undefined?

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13. What is a loop in JavaScript?

Answer:
A loop is used to repeat a block of code multiple times.

for(let i = 0; i < 3; i++) {
  console.log(i);
}

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14. What are the different types of loops in JavaScript?

• for

• while

• do...while

• for...of (for arrays)

• for...in (for objects)

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15. What is an object in JavaScript?

Answer:
An object is a collection of key: value pairs.

let person = { name: "Amit", age: 25 };

You can access values using person.name.

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16. What is the use of typeof operator?

Answer:
It tells the type of a value.

typeof 5        // "number"
typeof "hello"  // "string"

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17. What are conditional statements in JavaScript?

They allow you to make decisions in code:

• if

• else

• else if

• switch

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18. What is hoisting in JavaScript?

Answer:
Hoisting is JavaScript’s default behavior of moving declarations to the top of the current scope.

console.log(a); // undefined
var a = 5;

Variables declared with var are hoisted, but not let or const.

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19. What is scope in JavaScript?

Answer:
Scope refers to where variables are accessible in your code:

• Global scope

• Function scope

• Block scope

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20. What is a callback function?

Answer:
A callback is a function passed into another function to run later.

function greet(name, callback) {
  console.log("Hi " + name);
  callback();
}
greet("Payal", () => console.log("Welcome!"));

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21. What are template literals?

Answer:
Template literals use backticks (` ) to embed expressions:

let name = "Payal";
console.log(`Hello, ${name}!`);

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22. What is the difference between let and const?

• Use let when you might change the value.

• Use const when you never want to change the value.

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23. What are truthy and falsy values in JavaScript?

• Truthy: Values that behave like true in conditions (e.g., "hello", 1, [])

• Falsy: Behave like false (0, "", null, undefined, false, NaN)

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24. What is NaN in JavaScript?

Answer:
NaN stands for Not-a-Number. It appears when a math operation fails:

let x = "abc" / 2; // NaN

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25. What is event handling in JavaScript?

Answer:
Event handling allows you to respond to user actions, like clicks or keypresses.

button.addEventListener("click", () => {
  alert("Clicked!");
});

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26. What is a comment in JavaScript?

Used to write notes in your code.

// Single-line comment

/*
Multi-line
comment
*/

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27. What is a switch statement?

Used when you have multiple conditions to check.

switch (fruit) {
  case "Apple": console.log("Red"); break;
  case "Banana": console.log("Yellow"); break;
}

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28. What is the difference between for...in and for...of?

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29. What is the spread operator (...) in JavaScript?

It expands arrays or objects.

let arr = [1, 2, 3];
let newArr = [...arr, 4]; // [1,2,3,4]

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30. What are default parameters?

If no value is passed, a default is used.

function greet(name = "Guest") {
  console.log(`Hello, ${name}`);
}
greet(); // Hello, Guest

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🟢 Conclusion:

These 30 JavaScript questions are commonly asked in frontend interviews and are perfect for freshers. Understanding these concepts will give you a strong foundation for your career and help you speak confidently in interviews.

Next, we’ll move to Part 8, where we’ll tackle 30 advanced-level JavaScript questions for experienced developers.

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