Arrays and Tuples

Type an array

T[] or Array<T> both mean an array of T.

const scores: number[] = [88, 92, 76];
scores.push(95);
console.log(scores.length);

Map and filter with types

Callback parameters are often inferred from the array element type.

const names = ["Ada", "Lin", "Sam"];
const short = names.filter((name) => name.length <= 3);
console.log(short);

Use a tuple for fixed positions

A tuple gives each index its own type. Useful for pairs like coordinates or CSV-like rows.

const point: [number, number] = [10, 20];
const entry: [string, number] = ["lessons", 18];
console.log(point[0], entry[1]);

Readonly when needed

• readonly number[] prevents push and assignment
• Tuples can be readonly [string, number]
• Prefer arrays when length varies
• Prefer tuples when position carries meaning