JavaScript Variables

What are Variables?

Variables are containers for storing data values. In JavaScript, you can declare variables using var, let, or const.

Declaring Variables

Using var (Legacy)

var name = "John";
var age = 25;

Using let (Modern)

let name = "John";
let age = 25;

Using const (Constants)

const PI = 3.14159;
const company = "The World of Computing According to Dave";

Variable Naming Rules

• Variable names can contain letters, digits, underscores, and dollar signs
• Must begin with a letter, underscore, or dollar sign
• Are case-sensitive (age and Age are different)
• Cannot use reserved words (if, else, for, etc.)
• Use camelCase for multi-word variables

Assigning Values

You can assign values to variables when you declare them, or later:

// Declare and assign
let x = 5;

// Declare first
let y;
y = 10;

// Multiple variables
let a = 1, b = 2, c = 3;

Variable Types

JavaScript variables can hold different types of data:

let name = "John";        // String
let age = 25;             // Number
let isStudent = true;       // Boolean
let hobbies = ["reading", "coding"];  // Array
let person = {name: "John", age: 25}; // Object

let vs const vs var

Best Practices

• Use const by default, let when you need to reassign
• Avoid using var in modern JavaScript
• Use meaningful variable names
• Initialize variables when declaring them
• Use camelCase for variable names