• Hajipur, Bihar, 844101

☰
❮
❯

JavaScript

JS Basics

JS Variables & Operators

JS Data Types & Conversion

JS Numbers & Math

JS Strings

JS Dates

JS Arrays

JS Control Flow

JS Loops & Iteration

JS Functions

JS Objects

JS Classes & Modules

JS Async Programming

JS Advanced

JS HTML DOM

JS BOM (Browser Object Model)

JS Web APIs

JS AJAX

JS JSON

JS Graphics & Charts

JavaScript

JS Basics

JS Variables & Operators

JS Data Types & Conversion

JS Numbers & Math

JS Strings

JS Dates

JS Arrays

JS Control Flow

JS Loops & Iteration

JS Functions

JS Objects

JS Classes & Modules

JS Async Programming

JS Advanced

JS HTML DOM

JS BOM (Browser Object Model)

JS Web APIs

JS AJAX

JS JSON

JS Graphics & Charts

JS Functions

← Previous Next →

📘 JavaScript Functions – Reusable Blocks of Code

A function is a set of statements that performs a task or returns a value. Functions help you write modular, DRY (Don't Repeat Yourself) code.

🔹 Syntax – Declaring a Function

function functionName(parameters) {
  // code to execute
}

  • functionName is the name you give to the function.

  • parameters are input values passed to the function.

  • return is used to send back a result.

🔹 Example 1 – Basic Function

function greet(name) {
  return "Hello, " + name;
}

console.log(greet("Alice")); // Output: Hello, Alice

🔹 Example 2 – Function Without Parameters

function sayHi() {
  console.log("Hi there!");
}

sayHi(); // Output: Hi there!

🔹 Function Expressions

const add = function(a, b) {
  return a + b;
};

console.log(add(2, 3)); // Output: 5

🔹 Arrow Functions (ES6+)

const multiply = (x, y) => x * y;

console.log(multiply(4, 5)); // Output: 20

🔹 Function with Default Parameters

function greet(name = "Guest") {
  return "Welcome, " + name;
}

console.log(greet()); // Output: Welcome, Guest

🔹 Function Return vs Console.log

  • return sends a value back to the caller.

  • console.log() just prints the value in the console.

Practice Questions

Q1. How do you define a named function in JavaScript?

Q2. What is the difference between a function declaration and a function expression?

Q3. How can you write a function that takes two numbers and returns their sum?

Q4. What is the purpose of the return statement in a function?

Q5. Write a function that takes a string and returns it in uppercase.

Q6. What are arrow functions, and how do they differ from regular functions?

Q7. How do default parameters work in JavaScript functions?

Q8. Can a function be stored in a variable? Show with an example.

Q9. What happens if a function is called with fewer arguments than parameters?

Q10. Write a function that calculates the factorial of a number using a loop.

JS Functions Quiz

Q1: Which keyword is used to define a function in JavaScript?

A. method
B. def
C. func
D. function

Q2: How can you call a function named myFunc?

A. call myFunc()
B. execute myFunc()
C. myFunc()
D. invoke(myFunc)

Q3: What does a function return if there’s no return statement?

A. 0
B. null
C. undefined
D. empty

Q4: Which of the following is a function expression?

A. function sayHello() {}
B. let sayHello = function() {}
C. const sayHello = () => {}
D. Both b and c

Q5: What are parameters in a function?

A. The function name
B. Default values
C. Variables listed inside parentheses in function definition
D. Values returned from a function

Q6: Which is a valid arrow function syntax?

A. () => { return 5; }
B. function => 5
C. () -> 5
D. arrow() => 5

Q7: What is the purpose of the return keyword in a function?

A. To stop the function
B. To jump to another function
C. To send a result back
D. To end the script

Q8: Which statement is true about functions in JavaScript?

A. Functions cannot be stored in variables
B. Functions can return only strings
C. Functions can be reused multiple times
D. Functions must always return a value
← Previous Next →
Login
Go Back Top