TS-5

• 交叉类型&：交集

type A = string & number // never

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• interface使用extends的话，发现有类型冲突会直接冲突，因此在定义可扩展的类型时最好用interface
• 函数的交集会得到参数的并集

type A = {
  method: (n:string) => void
}

type B = {
  method: (n:number) => void
} & A

const x:B = {
  // n:string | number
  method:(n)=>{
   console.log(n);
  }
}

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type Fn1 = (n:string) => void
type Fn2 = (n:number) => void
type Fn = Fn1 & Fn2
// n: string | number
const fn: Fn = (n)=> console.log();

• 具体理解 |，ts声明时检查紧，赋值时检查松

type A = {
  name: string
}

type B = {
  age: number
}

type C = A | B

// 都正确
const p:C = {name:'x'}
const p:C = {age: 12}

// error，不能有gender属性
const x:C = {
  name:'',
  age: 12,
  gender: ''
}
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// 不报错
const d = {
  name: '',
  age: 12,
  gender: '' 
}
const p:C = d