Snippets Typescript

getUnionTypeFromStringArray.ts

const roles = ['read', 'write', 'readAndWrite'] as const;

type Roles = typeof roles[number]; 
// equals to this
// type Roles = "read" | "write" | "readAndWrite"

// or even like this
type RolesInCapital = Capitalize<typeof roles[number]>;
// equals to this
// type RolesInCapital = "Read" | "Write" | "ReadAndWrite"

unpackArray.ts

// The `infer` keyword
const User = {
  id: 123,
  username: 'John',
  email: 'john@gmail.com',
  addons: [
    { name: 'WriteAddon', id: 1 },
    { name: 'TodoAddon', id: 2 }
  ]
};


type UnpackArray<T> = T extends (infer R)[] ? R: T;

type AddonType = UnpackArray<typeof User.addons>; // { name: string, id: number }