JavaScript Functions – Introduction

Last Updated: 21st October 2025

  • A function is a block of code designed to perform a specific task.
  • Functions only run when called.
  • They help you organize code and reuse logic without rewriting it.

Hinglish Tip 🗣: Function ko aise samjho—ek “machine” jisme input (parameters) jaata hai aur output (return value) milta hai. Ek baar banao, baar-baar use karo.

Why Use Functions?

  1. Reusability – Write once, use many times.
  2. Modularity – Divide your code into smaller, manageable blocks.
  3. Readability – Makes code easier to read and maintain.
  4. Abstraction – Hide complex logic behind a simple function call.

Real-Life Analogy

Imagine a coffee machine:

  • Input → Coffee powder + water + milk
  • Process → Machine brews the coffee
  • Output → Cup of coffee ready

Similarly, in JS:

function makeCoffee(coffeeType) {
  return `Your ${coffeeType} coffee is ready!`;
}

console.log(makeCoffee("Espresso"));
// Output: Your Espresso coffee is ready!

Hinglish Tip 🗣: Jaise coffee machine me alag-alag inputs daal kar alag-alag coffee banate hain, JS me function me arguments daal kar alag outputs lete hain.

Type of Functions

There are two types of functions:

  • User-Defined Functions: Created by you.
  • Built-in Functions: Part of the JavaScript Standard Library.

User-Defined Functions

Built-in Functions

Built-in functions are part of the JavaScript Standard Library and you can use them without installing any additional packages. Some of them are: console.log(), document.getElementById(), setTimeout(), setInterval(), etc.

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