TS内置类型总结

1. typeof 取对象身上的类型

   const person = {name: '',job: '',age:18
   }
   type p = typeof person
   ->>
   type p = {name: string;job: string;age: number;
   }
   

2. keyof取一个类型的属性明作为一个联合类型

   1. const person = {name: '',job: '',age: 18
      }
      type p = typeof person
      type k = keyof p 
      --》》
      type k = "name" | "job" | "age"
      

3. Partial将传入的泛型中每个属性都变成可选属性

   1. 源码
      type Par<T> = {[P in keyof T]?:T[P]
      }interface person  {name: string,job: string,age: number
      }
      type a = Partial<person>
      -》》
      type a = {name?: string | undefined;job?: string | undefined;age?: number | undefined;
      }
      

4. Pick在传入泛型T中筛选出指定属性K的类型

   1. 源码
      type Pick<T,K extends keyof T> = {[P in K]:T[P]
      }interface person {name: string,job: string,age: number
      }
      type pick = Pick<person, 'age'>
      ——》》
      interface person {name: string,job: string,age: number
      }
      

5. Record将泛型K作为属性名（K可是联合类型） T作为属性类型

   1. type Record<K extends keyof any,T> = {[P in K]:T
      }
      keyof any = ->>> string | number | symbolinterface person {name: string,job: string,age: number
      }
      type human = 'name' | 'job'
      type record = Record<human, person>
      type record = {name: person;job: person;
      }
      

6. Readonly将传入的泛型全部属性变成只读

   1. type Readonly<T> = {readonly [P in keyof T]:T[P]
      }interface person {name: string,job: string,age: number
      }
      type readonly = Readonly<person>
      --->
      type readonly = {readonly name: string;readonly job: string;readonly age: number;
      }
      

7. infer：如果传入泛型T是数组类型就取数组元素的类型否则传入什么类型返回什么类型

   1. type TYPE<T> = T extends Array<infer U> ? U : T
      type t = TYPE<(number|string)[]>