阅读提示：
每个方法都有相应的描述、语法、参数、返回值、注意项（可选）、例子（可选）。
语法中的[]里面中的内容表示参数为可选参数。

Array.from()

描述：从一个类似数组或可迭代对象中创建一个新的数组实例。

语法：

new_array = Array.from(arrayLike[, callback(element[, index[, array]])[, thisArg]]);

1042 - IsNever

by hiroya iizuka (@hiroyaiizuka) #中等 #union #utils

题目

Implement a type IsNever, which takes input type T.
If the type of resolves to never, return true, otherwise false.

For example:

type A = IsNever<never> // expected to be true
type B = IsNever<undefined> // expected to be false
type C = IsNever<null> // expected to be false
type D = IsNever<[]> // expected to be false
type E = IsNever<number> // expected to be false

1097 - IsUnion

by null (@bencor) #中等 #union

题目

Implement a type IsUnion, which takes an input type T and returns whether T resolves to a union type.

For example:

type case1 = IsUnion<string> // false
type case2 = IsUnion<string | number> // true
type case3 = IsUnion<[string | number]> // false

1130 - ReplaceKeys

by 贱贱 (@lullabyjune) #中等 #object-keys

题目

Implement a type ReplaceKeys, that replace keys in union types, if some type has not this key, just skip replacing,
A type takes three arguments.

For example:

type NodeA = {
  type: "A"
  name: string
  flag: number
}

type NodeB = {
  type: "B"
  id: number
  flag: number
}

type NodeC = {
  type: "C"
  name: string
  flag: number
}

type Nodes = NodeA | NodeB | NodeC

type ReplacedNodes = ReplaceKeys<
  Nodes,
  "name" | "flag",
  { name: number; flag: string }
> // {type: 'A', name: number, flag: string} | {type: 'B', id: number, flag: string} | {type: 'C', name: number, flag: string} // would replace name from string to number, replace flag from number to string.

type ReplacedNotExistKeys = ReplaceKeys<Nodes, "name", { aa: number }> // {type: 'A', name: never, flag: number} | NodeB | {type: 'C', name: never, flag: number} // would replace name to never

1367 - Remove Index Signature

by hiroya iizuka (@hiroyaiizuka) #中等 #object-keys

题目

Implement RemoveIndexSignature<T> , exclude the index signature from object types.

For example:

type Foo = {
  [key: string]: any
  foo(): void
}

type A = RemoveIndexSignature<Foo> // expected { foo(): void }

1978 - Percentage Parser

by SSShuai1999 (@SSShuai1999) #中等 #template-literal

题目

实现类型 PercentageParser<T extends string>。根据规则 /^(\+|\-)?(\d*)?(\%)?$/ 匹配类型 T。

匹配的结果由三部分组成，分别是：[正负号, 数字, 单位]，如果没有匹配，则默认是空字符串。

2070 - Drop Char

by CaptainOfPhB (@CaptainOfPhB) #中等 #template-literal #infer

题目

从字符串中剔除指定字符。

例如：

type Butterfly = DropChar<' b u t t e r f l y ! ', ' '> // 'butterfly!'

2257 - MinusOne

by Mustafo Faiz (@fayzzzm) #中等 #math

题目

给定一个正整数作为类型的参数，要求返回的类型是该数字减 1。

例如:

type Zero = MinusOne<1> // 0
type FiftyFour = MinusOne<55> // 54

2595 - PickByType

by jiangshan (@jiangshanmeta) #中等 #object

题目

From T, pick a set of properties whose type are assignable to U.

For Example

type OnlyBoolean = PickByType<{
  name: string
  count: number
  isReadonly: boolean
  isEnable: boolean
}, boolean> // { isReadonly: boolean; isEnable: boolean; }

2688 - StartsWith

by jiangshan (@jiangshanmeta) #中等 #template-literal

题目

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:

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