✅ Boolean,null,undefined Data Type

Last Updated: 8th Oct 2025

Booleans Data Type

  • A Boolean data type represents only two values → true or false.
  • It is often used in conditions, comparisons, or logical decisions in a program.
  • Think of it as an ON/OFF switch — either something is or is not.

Hinglish Tip 🗣: Boolean matlab sirf do hi jawab — “Haan (true)” ya “Nahi (false)”. JavaScript me ye decision lene ke kaam aata hai jaise condition check karna.

let isOnline = true;
let isLightOn = false;

console.log(isOnline); // true
console.log(isLightOn); // false
console.log(typeof isOnline); // "boolean"

Null Data Type

  • A null value represents the absence of any object value.
  • It is often used to represent a missing or unknown value in a program.
  • Think of it as a placeholder for a missing value.
let user = null;

console.log(user); // null
console.log(typeof user); // "object"

Undefined Data Type

  • An undefined value represents the absence of a value.
  • It is often used to represent a variable that has not been assigned a value yet.
  • Think of it as a variable that has not been initialized yet.
let age;

console.log(age); // undefined
console.log(typeof age); // "undefined"

🧠 Truthy and Falsy Values

In JavaScript, some values automatically act as true or false in conditions — even if they are not explicitly true or false.

Falsy Values (act as false):

  • false
  • 0
  • "" (empty string)
  • null
  • undefined
  • NaN (Not a Number)

Truthy Values (act as true):

  • true
  • Any number (except 0)
  • Any string (except the empty string)
  • Any object
  • Any array (except the empty array)

Hinglish Tip 🗣: JavaScript me sab kuch clearly true/false nahi hota — kuch values “truthy” aur kuch “falsy” behave karti hain. Ye condition me automatic conversion hota hai.

🎯 Exercises

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