JavaScript Fundamentals

Variables and Data Types

Understanding Variables and Data Types

Variables are containers for storing data values. JavaScript provides several ways to declare variables and supports various data types to handle different kinds of information.

Variable Declarations

// Variable declarations
let name = "John";           // String
const age = 25;             // Number
var isStudent = true;       // Boolean
let scores = [85, 92, 78];  // Array
let person = {              // Object
  name: "John",
  age: 25
};

Data Types

// JavaScript Data Types
let string = "Hello";       // String
let number = 42;           // Number
let boolean = true;        // Boolean
let array = [1, 2, 3];     // Array
let object = {};          // Object
let nullValue = null;     // Null
let undefinedValue;       // Undefined

Modern JavaScript Features

// Modern JavaScript Features
const PI = 3.14;           // Constants
let [x, y] = [1, 2];      // Array Destructuring
let { name, age } = person; // Object Destructuring
let sum = (...nums) => nums.reduce((a, b) => a + b); // Rest Parameters