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TrimLeft

介绍​

实现 TrimLeft<T> ，它接收确定的字符串类型并返回一个新的字符串，其中新返回的字符串删除了原字符串开头的空白字符串。

例如

ts
  
type trimed = TrimLeft<'  Hello World  '> // 应推导出 'Hello World  '
ts
  
type trimed = TrimLeft<'  Hello World  '> // 应推导出 'Hello World  '
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type TrimLeft<T> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<TrimLeft<'str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<' str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'     str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'     str     '>, 'str     '>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'   \n\t foo bar '>, 'foo bar '>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<''>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<' \n\t'>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type TrimLeft<T> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<TrimLeft<'str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<' str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'     str'>, 'str'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'     str     '>, 'str     '>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<'   \n\t foo bar '>, 'foo bar '>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<''>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<TrimLeft<' \n\t'>, ''>>,
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
//方法1
type Whitespace = ' ' | '\n'| '\t'
type TrimLeft<S extends string> = S extends `${Whitespace}${infer Rest}` ? TrimLeft<Rest> : S;
 
ts
//方法1
type Whitespace = ' ' | '\n'| '\t'
type TrimLeft<S extends string> = S extends `${Whitespace}${infer Rest}` ? TrimLeft<Rest> : S;
 
ts
// 潜在问题: 
/**
 * TypeScript 中的递归类型确实存在深度限制。TypeScript 默认的递归深度限制约为 45-50 层，具体限制可能因版本而略有不同。当递归嵌套达到这个限制时，TypeScript 编译器会报错。
 * 
 * 思路
 * 1.尾递归优化
 *  - 减少递归次数
 *  - 优化效果有限
 * 2.分段处理
 *  - 
 * 
 */
// 尾递归优化
 
type TrimRight<T extends string> = 
  T extends `${infer Rest} ` ? TrimRight<Rest> :
  T extends `${infer Rest}\n` ? TrimRight<Rest> :
  T extends `${infer Rest}\t` ? TrimRight<Rest> :
  T;
 
ts
// 潜在问题: 
/**
 * TypeScript 中的递归类型确实存在深度限制。TypeScript 默认的递归深度限制约为 45-50 层，具体限制可能因版本而略有不同。当递归嵌套达到这个限制时，TypeScript 编译器会报错。
 * 
 * 思路
 * 1.尾递归优化
 *  - 减少递归次数
 *  - 优化效果有限
 * 2.分段处理
 *  - 
 * 
 */
// 尾递归优化
 
type TrimRight<T extends string> = 
  T extends `${infer Rest} ` ? TrimRight<Rest> :
  T extends `${infer Rest}\n` ? TrimRight<Rest> :
  T extends `${infer Rest}\t` ? TrimRight<Rest> :
  T;
 
ts
// Trim
type Whitespace = ' ' | '\n'| '\t'
type TrimLeft<S extends string> = S extends `${Whitespace}${infer Rest}` ? TrimLeft<Rest> : S;
type TrimRight<S extends string> = S extends `${infer F}${Whitespace}` ? TrimRight<F> : S;
type Trim<S extends string> = TrimLeft<TrimRight<S>>
 
ts
// Trim
type Whitespace = ' ' | '\n'| '\t'
type TrimLeft<S extends string> = S extends `${Whitespace}${infer Rest}` ? TrimLeft<Rest> : S;
type TrimRight<S extends string> = S extends `${infer F}${Whitespace}` ? TrimRight<F> : S;
type Trim<S extends string> = TrimLeft<TrimRight<S>>
 
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