JavaScript Basics

Variables

JavaScript provides three ways to declare variables: var, let, and const. let and const are block‑scoped, while var is function‑scoped.

let name = "Alice";
const PI = 3.14159;
var count = 0;

Functions

Functions are reusable blocks of code. They can be declared in several ways:

// Function Declaration
function greet(person) {
  return `Hello, ${person}!`;
}

// Function Expression
const square = function(x) {
  return x * x;
};

// Arrow Function
const add = (a, b) => a + b;

Loops

Loops let you repeat actions. JavaScript supports for, while, and do…while loops.

for (let i = 0; i < 5; i++) {
  console.log(i);
}

let j = 0;
while (j < 5) {
  console.log(j);
  j++;
}

Try It Yourself

Write JavaScript code in the editor below and see the output instantly.