TS-2 enum

• enum只用来声明数字就行了，字符串用联合类型最好，enum的值不能是对象类型
• enum

enum A = {
  todo = 0,
  done, // 1
  deleted // 2
}

let status1 = A.todo
let status2 = 0

• 用 enum 处理权限问题

enum Permission = {
  None = 0,
  Read = 1 << 0,      // 0001
  Write = 1 << 1,     // 0010
  Delete = 1 << 2,    // 0100
  Manage  = 1 << 3    // 1000
}

type User = {
  permission: Permission
}

const user: User = {
  permission: 0b0101
}

if(CanWrite(user.permission)){
  console.log('有写权限')
}
if(CanManage(user.permission)){
  console.log('有管理权限')
}
function CanWrite(p:Permission){
  return (p & Permission.Write) === Permission.Write
}
function CanManage(p:Permission){
  return (p & Permission.Manage) === Permission.Manage 
}