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TypeScript Cheat Sheet — Types Reference

The TypeScript syntax you use most, from basic annotations to generics and utility types.

Put it into practice with the matching tool.

Basic types

let n: numberNumber

let s: stringString

let b: booleanBoolean

let a: string[]Array of strings (or Array<string>)

let t: [string, number]Tuple — fixed length and types

let u: unknownUnknown — must be narrowed before use

let v: neverNever — a value that cannot occur

interface User { id: number; name: string }Describe an object shape

name?: stringOptional property

readonly id: numberCannot be reassigned

type User = { id: number }Type alias — same idea, more flexible

interface Admin extends User {}Extend another interface

[key: string]: numberIndex signature for arbitrary keys

(a: number): string => {}Typed parameters and return

(a: number, b = 2) => {}Default parameter

(...args: number[]) => {}Rest parameters

(): voidReturns nothing

type Fn = (a: string) => numberFunction type alias

type S = 'a' | 'b'Union of literal types

string | nullValue may be null

A & BIntersection — has both shapes

typeof x === 'string'Narrow a union at runtime

x as stringType assertion (use sparingly)

x!Non-null assertion

function f<T>(x: T): TGeneric function

Partial<T>All properties optional

Required<T>All properties required

Pick<T, "a" | "b">Keep only these keys

Omit<T, "a">Remove these keys

Record<string, number>Object with typed keys and values

ReturnType<typeof fn>The return type of a function

Typing API Responses: From JSON to TypeScript Types