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IndexOf

介绍​

实现数组的IndexOf类型, indexOf<T,U>接收数组T, 任意U, 返回U在T中第一次出现的索引

ts
  type Res = IndexOf<[1, 2, 3], 2>; // expected to be 1
type Res1 = IndexOf<[2,6, 3,8,4,1,7, 3,9], 3>; // expected to be 2
type Res2 = IndexOf<[0, 0, 0], 2>; // expected to be -1
ts
  type Res = IndexOf<[1, 2, 3], 2>; // expected to be 1
type Res1 = IndexOf<[2,6, 3,8,4,1,7, 3,9], 3>; // expected to be 2
type Res2 = IndexOf<[0, 0, 0], 2>; // expected to be -1
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type IndexOf<T, U> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<IndexOf<[1, 2, 3], 2>, 1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[2, 6, 3, 8, 4, 1, 7, 3, 9], 3>, 2>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[0, 0, 0], 2>, -1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 1, number, 'a'], number>, 2>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 1, number, 'a', any], any>, 4>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 'a'], 'a'>, 1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[any, 1], 1>, 1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
ts
/* _____________ Your Code Here _____________ */
 
type IndexOf<T, U> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<IndexOf<[1, 2, 3], 2>, 1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[2, 6, 3, 8, 4, 1, 7, 3, 9], 3>, 2>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[0, 0, 0], 2>, -1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 1, number, 'a'], number>, 2>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 1, number, 'a', any], any>, 4>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[string, 'a'], 'a'>, 1>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<IndexOf<[any, 1], 1>, 1>>,
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 IndexOf<T extends any[],U, X extends number = number> = U extends T[number]
  ? {[X in keyof T as X extends `${number}` ? (T[X] extends U ? U : never) : never ] : X}[U]
  : -1
 
ts
type IndexOf<T extends any[],U, X extends number = number> = U extends T[number]
  ? {[X in keyof T as X extends `${number}` ? (T[X] extends U ? U : never) : never ] : X}[U]
  : -1
 
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