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Parameters

介绍​

实现内置的Parameters泛型而不使用它.

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start point​

ts
/* _____________ Your Code Here _____________ */
type MyParameters<T extends (...args: any[]) => any> = any;
 
/* _____________ Test Cases _____________ */
const foo = (arg1: string, arg2: number): void => {};
const bar = (arg1: boolean, arg2: { a: 'A' }): void => {};
const baz = (): void => {};
 
type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: 'A' }]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<MyParameters<typeof baz>, []>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
];
ts
/* _____________ Your Code Here _____________ */
type MyParameters<T extends (...args: any[]) => any> = any;
 
/* _____________ Test Cases _____________ */
const foo = (arg1: string, arg2: number): void => {};
const bar = (arg1: boolean, arg2: { a: 'A' }): void => {};
const baz = (): void => {};
 
type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: 'A' }]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<MyParameters<typeof baz>, []>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
];
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my solution​

Spoiler warning // Click to reveal answer
ts
type MyParameters<T extends (...args: any[]) => any> = T extends (...args: infer T) => any
  ? T
  : never;
ts
type MyParameters<T extends (...args: any[]) => any> = T extends (...args: infer T) => any
  ? T
  : never;
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