TypeScript联合类型和类型保护-蒲公英云

TypeScript联合类型和类型保护

r囧r小猫 2023-07-23 06:57 81阅读 0赞

TypeScript在使用联合类型时，会遇到以下问题，需要进行类型保护，以保证逻辑严谨性。

// 联合类型
// 用于进行类型保护的方式
// 1. as 语法 - 类型断言
interface Bird { 
  fly: boolean;
  sing: () => { };
}
interface Dog { 
  fly: boolean;
  bark: () => { };
}
const trainAnimal = (animal: Bird | Dog) => { 
  animal.fly ? (animal as Bird).sing() : (animal as Dog).bark();
};
// 2. in 语法
const trainAnimalSecond = (animal: Bird | Dog) => { 
  'sing' in animal ? animal.sing() : animal.bark();
};
// 3. typeof 语法
const addData = (first: string | number, second: string | number) => { 
  return typeof first === 'string' || typeof second === 'string'
    ? `${ first}${ second}`
    : first + second;
};
// 4. instanceof 语法
class NumberObj { 
  constructor(public count: number) { }
}
const addDataSecond = (
  first: object | NumberObj,
  second: object | NumberObj
) => { 
  return first instanceof NumberObj && second instanceof NumberObj
    ? first.count + second.count
    : 0;
};