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StartsWith

介绍​

实现StartsWith<T, U>,接收两个string类型参数,然后判断T是否以U开头,根据结果返回true或false

例如：

ts
type a = StartsWith<'abc', 'ac'> // expected to be false
type b = StartsWith<'abc', 'ab'> // expected to be true
type c = StartsWith<'abc', 'abcd'> // expected to be false
ts
type a = StartsWith<'abc', 'ac'> // expected to be false
type b = StartsWith<'abc', 'ab'> // expected to be true
type c = StartsWith<'abc', 'abcd'> // expected to be false
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type StartsWith<T extends string, U extends string> = any;
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<StartsWith<'abc', 'ac'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'ab'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'abc'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'abcd'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', ''>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', ' '>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'', ''>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type StartsWith<T extends string, U extends string> = any;
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<StartsWith<'abc', 'ac'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'ab'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'abc'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', 'abcd'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', ''>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'abc', ' '>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<StartsWith<'', ''>, true>>,
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 StartsWith<T extends string, U extends string> = T extends `${U}${string}` ? true : false;
 
ts
type StartsWith<T extends string, U extends string> = T extends `${U}${string}` ? true : false;
 
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