TypeScript 中的联合类型和类型保护

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本节介绍 ts 中的联合类型和类型保护的几种方法

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interface CustomModel {
  goods: boolean;
  name: string;
  age: number;
  buy: () => {};
}

interface MerchantModel {
  goods: boolean;
  name: string;
  age: number;
  sell: () => {};
}

as 断言

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function judgePeopleAs(people: CustomModel | MerchantModel) {
  if (people.goods) {
    (people as MerchantModel).sell();
  } else {
    (people as CustomModel).buy();
  }
}

in 断言

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function judgePeopleIn(people: CustomModel | MerchantModel) {
  if ("buy" in people) {
    people.buy();
  } else {
    people.sell();
  }
}

typeof 类型检查

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function addStrOrNum(first: string | number, second: string | number) {
  if (typeof first === "string" || typeof second === "string") {
    return `${first}  ${second}`;
  }
  return first + second;
}

instanceof （只能用在类中）

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class NumberObj {
  count: number = 0;
}

function AddObj(first: object | NumberObj, second: object | NumberObj) {
  if (first instanceof NumberObj && second instanceof NumberObj) {
    return first.count + second.count;
  }
  return 0;
}