https://mp.weixin.qq.com/s/4tM37jZDHftkWKvGncVgIw

1，原理是只有nerver才能赋值给never

如果你漏处理了一个类型，导致它没有被认领，就会报类型错误；

declare enum Color {
  Red,
  Yellow,
  Blue,
  Pink,
}

declare let color: Color;

switch (color) {
  case Color.Red:
    // do something
    break;

  case Color.Yellow:
    // do something
    break;

  case Color.Blue:
    // do something
    break;

  default:
    // 不能将类型“Color”分配给类型“never”。
    let exhaustiveCheck: never = color;

    break;
}

2. 使用”互斥“替代”联合“类型;

适用于”转换按钮“这样的场景

type XORUser = XOR<Visitor, Registered>;

”要么同时有，要么同时没有“

interface Registered {
  email: string;
  registerTime: number;
  level: number;
}

type XORStruct = XOR<{}, Registered>;

const val1: XORStruct = {}; // √

// X
const val2: XORStruct = {
  email: '[email protected]',
};

// √
const val3: XORStruct = {
  email: '[email protected]',
  registerTime: Date.now(),
  level: 9999,
};

3. (string & {}) 交叉，就不会出现PresetSize被合并进string的情况了

type PresetSize = 'mini' | 'middle' | 'large';

type Size = PresetSize | (string & {});

let size1: Size = 'mini';
let size2: Size = '200px';