Typescript Hints

typescript.ts

// use the strings in an array as types.
const animals = ["cat", "dog", "mouse"] as const
type Animal = (typeof animals)[number] // transformer like "cat" | "dog" | ...
let myAnimal : Animal = "cat" // <- autocomplete works here

// merge two types.
type Prefix = "sub_"
type Numbers = 0 | 1 | 2 | 3 | 4 | 5
type SubNumbers = `${Prefix}${Numbers}` // transforms to sub_1 | sub_2 | ...
let myNumber : SubNumbers = "sub_0" // <- autocomplete works here

// objects instead of enums.
const Roles = {
  Admin: "admin",
  Writer: "writer",
  Reader: "reader"
} as const

// Convert object key in a type
type RoleKeys = (typeof Roles)[keyof typeof Roles]
declare function hasAccess(role: RoleKeys): void
hasAccess("admin") // works, but no auto-refactoring of keys. would not work with an enum.
hasAccess(Roles.Admin) // 👍 works with auto-refactoring.