Capitalize

介绍

实现 Capitalize<T> 它将字符串的第一个字母转换为大写，其余字母保持原样。

例如

ts
  
type capitalized = MyCapitalize<'hello world'> // expected to be 'Hello world'

ts
  
type capitalized = MyCapitalize<'hello world'> // expected to be 'Hello world'

View on GitHub

起点

ts
/* _____________ Your Code Here _____________ */
 
type MyCapitalize<T> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
Expect<Equal<MyCapitalize<'foobar'>, 'Foobar'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'FOOBAR'>, 'FOOBAR'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'foo bar'>, 'Foo bar'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<''>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'a'>, 'A'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'b'>, 'B'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'c'>, 'C'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'d'>, 'D'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'e'>, 'E'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'f'>, 'F'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'g'>, 'G'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'h'>, 'H'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'i'>, 'I'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'j'>, 'J'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'k'>, 'K'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'l'>, 'L'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'m'>, 'M'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'n'>, 'N'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'o'>, 'O'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'p'>, 'P'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'q'>, 'Q'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'r'>, 'R'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'s'>, 'S'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'t'>, 'T'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'u'>, 'U'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'v'>, 'V'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'w'>, 'W'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'x'>, 'X'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'y'>, 'Y'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'z'>, 'Z'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.]

ts
/* _____________ Your Code Here _____________ */
 
type MyCapitalize<T> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
Expect<Equal<MyCapitalize<'foobar'>, 'Foobar'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'FOOBAR'>, 'FOOBAR'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'foo bar'>, 'Foo bar'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<''>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'a'>, 'A'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'b'>, 'B'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'c'>, 'C'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'d'>, 'D'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'e'>, 'E'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'f'>, 'F'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'g'>, 'G'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'h'>, 'H'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'i'>, 'I'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'j'>, 'J'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'k'>, 'K'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'l'>, 'L'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'m'>, 'M'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'n'>, 'N'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'o'>, 'O'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'p'>, 'P'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'q'>, 'Q'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'r'>, 'R'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'s'>, 'S'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'t'>, 'T'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'u'>, 'U'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'v'>, 'V'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'w'>, 'W'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'x'>, 'X'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'y'>, 'Y'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<MyCapitalize<'z'>, 'Z'>>,
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
 
// 注意: 原答案链接中,讨论了`${infer F}${infer Rest}` 和 `${infer F}${infer T}${infer Rest}`的区别. TS版本5测试来看,已经没有之前的特征
type azToAZ = {
  a: 'A',
  b: 'B',
  c: 'C',
  d: 'D',
  e: 'E',
  f: 'F',
  g: 'G',
  h: 'H',
  i: 'I',
  j: 'J',
  k: 'K',
  l: 'L',
  m: 'M',
  n: 'N',
  o: 'O',
  p: 'P',
  q: 'Q',
  r: 'R',
  s: 'S',
  t: 'T',
  u: 'U',
  v: 'V',
  w: 'W',
  x: 'X',
  y: 'Y',
  z: 'Z'
}
 
type UpperCase<T extends string> = T extends keyof azToAZ ? azToAZ[T] : T;
 
type MyCapitalize<T extends string> = T extends `${infer F}${infer Rest}` ? `${UpperCase<F>}${Rest}` : T;

ts
//方法1
 
// 注意: 原答案链接中,讨论了`${infer F}${infer Rest}` 和 `${infer F}${infer T}${infer Rest}`的区别. TS版本5测试来看,已经没有之前的特征
type azToAZ = {
  a: 'A',
  b: 'B',
  c: 'C',
  d: 'D',
  e: 'E',
  f: 'F',
  g: 'G',
  h: 'H',
  i: 'I',
  j: 'J',
  k: 'K',
  l: 'L',
  m: 'M',
  n: 'N',
  o: 'O',
  p: 'P',
  q: 'Q',
  r: 'R',
  s: 'S',
  t: 'T',
  u: 'U',
  v: 'V',
  w: 'W',
  x: 'X',
  y: 'Y',
  z: 'Z'
}
 
type UpperCase<T extends string> = T extends keyof azToAZ ? azToAZ[T] : T;
 
type MyCapitalize<T extends string> = T extends `${infer F}${infer Rest}` ? `${UpperCase<F>}${Rest}` : T;

ts
// most popular
type MyCapitalize<S extends string> = S extends `${infer x}${infer tail}` ? `${Uppercase<x>}${tail}` : S;

ts
// most popular
type MyCapitalize<S extends string> = S extends `${infer x}${infer tail}` ? `${Uppercase<x>}${tail}` : S;

ts
// second popular
interface ToUpperCase {
    a: "A"
    b: "B"
    c: "C"
    d: "D"
    e: "E"
    f: "F"
    g: "G"
    h: "H"
    i: "I"
    j: "J"
    k: "K"
    l: "L"
    m: "M"
    n: "N"
    o: "O"
    p: "P"
    q: "Q"
    r: "R"
    s: "S"
    t: "T"
    u: "U"
    v: "V"
    w: "W"
    x: "X"
    y: "Y"
    z: "Z"
}
 
type LowerCase = keyof ToUpperCase
type MyCapitalize<S extends string> = S extends `${infer First extends LowerCase}${infer Rest}` ? `${ToUpperCase[First]}${Rest}` : S

ts
// second popular
interface ToUpperCase {
    a: "A"
    b: "B"
    c: "C"
    d: "D"
    e: "E"
    f: "F"
    g: "G"
    h: "H"
    i: "I"
    j: "J"
    k: "K"
    l: "L"
    m: "M"
    n: "N"
    o: "O"
    p: "P"
    q: "Q"
    r: "R"
    s: "S"
    t: "T"
    u: "U"
    v: "V"
    w: "W"
    x: "X"
    y: "Y"
    z: "Z"
}
 
type LowerCase = keyof ToUpperCase
type MyCapitalize<S extends string> = S extends `${infer First extends LowerCase}${infer Rest}` ? `${ToUpperCase[First]}${Rest}` : S

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Capitalize

介绍​

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解决方案​

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解决方案