TypeScript 使用 union 类型实现 enum 类型

permissons.ts

// https://www.typescriptlang.org/play?#code/PTAEjztRRNMTwzDu3RaOUKe6gdeQFAGMD2A7AzgF1AAUBTAJwFsBLXXKnXUAXlAG9VRQySBDAEwBcoAOTd+wgDQdQAdzJV8JIcLkKSk6SQAeJdAFdFy7boPrUAX1A9GWPPgDcqfAE8ADiWLlqtetmagXd0wAM09KGjoGAG0AaxJnEIC3EkTScJ8GAF17UBARMT5hUAAfEVVFItLhY30KoA

// typescript playgroud 工作，实际项目中不工作
const permissions = ['read', 'write', 'execute'] as const;
type Permission = typeof permissions[number]; // 'read' | 'write' | 'execute'

// typescript playgroud 不工作，实际项目中工作
const Permissions = {
  read: 'read',
  write: 'write',
  execute: 'execute'
} as const;
type Permission = typeof Permissions[keyof typeof Permissions]; // 'read' | 'write' | 'execute'