JavaScript Fundamentals

JavaScript Basics

Beginner Lesson 2 of 10

JavaScript Basics

Master the building blocks of JavaScript programming.

Variables

// let - can be reassigned
let count = 0;
count = 1;

// const - cannot be reassigned
const PI = 3.14159;
// PI = 3; // Error!

// var - old way (avoid in modern JS)
var oldStyle = "legacy";

Data Types

// Primitive types
let str = "Hello";           // String
let num = 42;                // Number
let bool = true;             // Boolean
let undef = undefined;       // Undefined
let nothing = null;          // Null
let sym = Symbol("id");      // Symbol
let big = 9007199254740991n; // BigInt

// Reference types
let arr = [1, 2, 3];                    // Array
let obj = { name: "Alice", age: 25 };   // Object
let func = function() {};               // Function

Operators

// Arithmetic
let sum = 5 + 3;      // 8
let diff = 5 - 3;     // 2
let prod = 5 * 3;     // 15
let quot = 5 / 3;     // 1.666...
let rem = 5 % 3;      // 2
let pow = 5 ** 3;     // 125

// Comparison
5 == "5"    // true (loose equality)
5 === "5"   // false (strict equality - preferred!)
5 !== "5"   // true

// Logical
true && false  // false
true || false  // true
!true          // false

Strings

let name = "Alice";
let greeting = `Hello, ${name}!`; // Template literal

// String methods
"hello".toUpperCase();     // "HELLO"
"  hello  ".trim();        // "hello"
"hello".includes("ell");   // true
"hello".split("");         // ["h","e","l","l","o"]

Next Steps

Continue learning JavaScript with arrays, objects, and functions!