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Variables

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Variables are like labeled boxes where you store your stuff!

What are Variables?

A variable is a container that stores data. Think of it like a labeled box - you give it a name and put something inside.

Later, you can use the name to get the value back, or even change what's inside!

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Three Ways to Create Variables

JavaScript gives you three keywords to create variables:

const- Cannot be reassigned (use by default!)
let- Can be reassigned when needed
var- Old style, avoid using
1// const - value cannot change
2const name = "Alice";
3// name = "Bob"; // ERROR!
4
5// let - value can change
6let age = 25;
7age = 26; // OK!
8
9// var - old way, don't use
10var score = 100; // avoid this
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Data Types

Variables can hold different types of data:

1// String - text in quotes
2const greeting = "Hello, World!";
3
4// Number - integers and decimals
5const count = 42;
6const price = 19.99;
7
8// Boolean - true or false
9const isActive = true;
10const isGameOver = false;
11
12// Undefined - no value yet
13let username;
14console.log(username); // undefined
15
16// Null - intentionally empty
17const selectedItem = null;
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Try It Yourself!

Experiment with let and const below. Try reassigning values!

let messagecan change

Current value: "Hello"

const lockedcannot change
1let message = "Hello";
2const locked = "Cannot change me!";
3
4// You can change message:
5message = "New value"; // Works!
6
7// But not locked:
8// locked = "Try me"; // Error!

🧪 Code Lab - Try It Yourself!

🧪Variables Lab
Enter RunShift+Enter New line History
📋Output

Run some code to see the output here!

💡Try These Examples

Practice Exercises

3 exercises to master this lesson