为什么数字枚举可以分配给打字稿中的任何数字？

Question

我想知道为什么可以将数字枚举分配给任何数字。数字枚举和基于字符串的枚举有什么区别？

enum TYPES {
  False = 0,
  True = 1,
  UnKnow = 2,
}

type IType = {
  type: TYPES
}

const demo1: IType = {
  type: 9    // works, hope error: Type 9 is not assignable to type TYPES   
}

enum COLORS {
  GREEN = 'green',
  RED = 'red',
  YELLOW = 'yellow',
}

type IColor = {
  color: COLORS;
}

const demo2: IColor = {
  color: 'blue'   // error: Type '"blue"' is not assignable to type 'COLORS'.ts(2322)
}