TypeScript cheatsheet

typescript-cheatsheet.ts

// same arg type and return type
withUID<T>(obj: T)

// "extends" helps providing some constraints
// eg <T extends object>
withUID({a: 1}) // valid
withUID("wrong way") // NOT valid

// default value type (string)
A<T=string> { name: T }

// defining a type arg on top of another
MyFunc<T extends Person, S = T & { ssid: string }>(
  person: S
) : S {}
       
// overloads (have no body)
function getArray(...args: string[]): string[];
function getArray(args: number): undefined[];
function getArray(...args) {
}
       
// component
class MyComponent extends Component<Props, State> {
  state: State = {}
}

// partial subtype
type Partial<T> = { [P in keyof T]?: T[P]; }
type LocalUser = Partial<User>;
       
// exclude
Exclude<T, U>