Data Types in JS

JavaScript needs to know what kind of data it is working with so it knows what it can do with it. For example, you can multiply two Numbers, but you can't multiply two Sentences.

There are 7 "Primitive" data types in JS, but as a beginner, you only need to master the Big 5.

1. Strings (Text)

A String is just plain text. It must always be wrapped in quotes: single ' ', double " ", or backticks ` `.

• Analogy: Like a "string" of pearls, it is a sequence of characters linked together.
• Use for: Names, addresses, or any messages.

const name = "Ajay Dhangar";
const message = 'Welcome to CodeHarborHub';

2. Numbers (Math)

Unlike many other languages, JS only has one type for numbers. They can be whole integers or decimals. Do not use quotes for numbers, or JS will think they are text!

• Use for: Scores, prices, age, or calculations.

const age = 25;
const price = 9.99;

// Comparison:
const score = 10;   // This is a Number (You can do math with this)
const points = "10"; // This is a String (This is just a picture of a 10)

3. Booleans (Logic)

A Boolean can only be one of two values: true or false.

• Analogy: Like a light switch. It is either ON or OFF.
• Use for: Checking if a user is logged in, if a game is over, or if a checkbox is clicked.

let isDarkMode = true;
let isGameOver = false;

4. Undefined (The Empty Box)

When you create a variable but don't put anything in it yet, it is undefined.

• Analogy: You bought a box (variable), but it's still empty and waiting for content.

let mySecret;
console.log(mySecret); // Result: undefined

5. Null (The Intentional Nothing)

null is a value that represents "nothing" or "empty" on purpose.

• The Difference: undefined is an accidental empty box. null is you specifically saying, "This box is intentionally empty."

let userAwards = null; // The user has zero awards right now

Interactive Lab: The "Typeof" Tool

How do you check what is inside a variable? We use a special command called typeof.

Challenge Tasks:

1. In the JS tab, create a variable let test = "5";.
2. Use console.log(typeof test);. Is it a number or a string?
3. Remove the quotes around the 5. Check the typeof again. See the difference?

Pro Tip: Template Literals

When you want to mix a String with a Variable, use backticks ``` and the ${} syntax. It’s much easier than using the + sign!

index.js

const username = "Ajay";

// The old way (Hard)
console.log("Hello " + username + "!"); 

// The modern way (Easy)
console.log(`Hello ${username}!`); 

Summary Checklist

• I know that Strings must be inside quotes.
• I understand that Numbers do not use quotes.
• I know that Booleans are for True/False logic.
• I can use typeof to identify a data type.
• I understand the difference between null and undefined.