Implementing various type utilities in TypeScript

Apr 24, 2023#ts133

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1. The code is implementing the Partial type, which allows for optional properties in a given type. 2. The code is implementing the Pick type, which extracts specific properties from a given type. 3. The code is implementing the Extract type, which checks if a type is assignable to another type and returns the original type or never. 4. The code is implementing the Exclude type, which checks if a type is not assignable to another type and returns the original type or never. 5. The code is implementing the Record type, which creates an object with specified keys and values.

Implement Partial:

typeA={name:string,age:string}

type Partial<T>={
[p in keyof T]?:T[p]
}
//i.e. type C=Partial<A>

Implement pick to extract partial types

type example={name:string,age:number,address:string}
type Pick<T,U extends keyof T>={
  [P in U]=T[P]
}
const tiqu:Pick<example,"name"|"age">={}

Implement Extract

type Extract<T,U>=T extends U? T: never

type A=string | number | boolean
type B=string | number

type C=Extract<A,B>
const result:C="214214"
const result2:C=444

Implement Exclude, same idea as Extract

type Exclude<T,U>=T extends U?never :T
type A=string | number | boolean
type B=string | number

type C=Exclude<A,B>
const result:C="214214"  //error
const result2:C=true

Implement Record

type Record<K extends string|number|symbol,V>={
[P in K]:V
}
type EX=Record<'name'|'age',string|number>
const res:EX={name:"张三"，age:999}