TypeScript Cheat Sheet
Learn TypeScript from the basics →
Basic Types
let x: string = "hi";- Explicit type annotation
let x: number, y: boolean- Number and boolean types
let arr: number[] = [1, 2];- Typed array
let t: [string, number]- Tuple (fixed-length, typed positions)
Objects & Interfaces
interface User { name: string; age?: number }- Interface with an optional property
type ID = string | number;- Type alias (union type)
const u: User = { name: "Ada" };- Use an interface as a type
Functions
function f(x: number): string { }- Typed parameter and return value
function f(x?: number) { }- Optional parameter
const f = (x: number): number => x * 2;- Typed arrow function
Generics
function first<T>(arr: T[]): T { return arr[0]; }- Generic function
class Box<T> { value: T; }- Generic class
Special Types
any- Opts out of type checking (avoid)
unknown- Safer "any" — must be narrowed before use
never- A value that never occurs (e.g. always throws)
as Type- Type assertion (tell the compiler what you know)
Utility Types
Partial<User>- All properties optional
Pick<User, "name">- Only the listed properties
Omit<User, "age">- All properties except the listed ones
Readonly<User>- All properties read-only