Variables and functions

let, const, types, template strings and functions.

JavaScript runs in every browser and, with Node.js, on servers. Open the browser console (F12) and type the examples to try them.

const name = "Ana";     // cannot be reassigned
let score = 10;         // can change
score = score + 5;
console.log(`${name} has ${score} points`);

Prefer const, use let when the value changes, and avoid the old var.

Equality

CarefulUse === (strict equality), not ==. The loose == converts types: "5" == 5 is true, but "5" === 5 is false.

Functions

function add(a, b) { return a + b; }
const double = (n) => n * 2;      // arrow function
console.log(add(2, 3), double(4)); // 5 8