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PickByType

介绍​

从类型'T'中, 筛选出属性类型位'U'的集合

例如：

ts
type OnlyBoolean = PickByType<{
  name: string
  count: number
  isReadonly: boolean
  isEnable: boolean
}, boolean> // { isReadonly: boolean; isEnable: boolean; }
ts
type OnlyBoolean = PickByType<{
  name: string
  count: number
  isReadonly: boolean
  isEnable: boolean
}, boolean> // { isReadonly: boolean; isEnable: boolean; }
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type PickByType<T, U> = any
 
/* _____________ Test Cases _____________ */
 
interface Model {
  name: string
  count: number
  isReadonly: boolean
  isEnable: boolean
}
type cases = [
  Expect<Equal<PickByType<Model, boolean>, { isReadonly: boolean, isEnable: boolean }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<PickByType<Model, string>, { name: string }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<PickByType<Model, number>, { count: number }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type PickByType<T, U> = any
 
/* _____________ Test Cases _____________ */
 
interface Model {
  name: string
  count: number
  isReadonly: boolean
  isEnable: boolean
}
type cases = [
  Expect<Equal<PickByType<Model, boolean>, { isReadonly: boolean, isEnable: boolean }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<PickByType<Model, string>, { name: string }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<PickByType<Model, number>, { count: number }>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
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解决方案​

Spoiler warning // Click to reveal answer
ts
type PickByType<T, U> = {
  [K in keyof T as T[K] extends U ? K : never]: T[K]
}
 
ts
type PickByType<T, U> = {
  [K in keyof T as T[K] extends U ? K : never]: T[K]
}
 
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