对 ts 的掌握一定要 练，如果在开发中没有条件的话，这有个宝藏的 Github项目🌟 type-challenges
Warm-up
1. Hello World
// expected to be string
type HelloWorld = any
// answer
type HelloWorld = string
Easy
1. Pick
interface Todo {
title: string
description: string
completed: boolean
}
type TodoPreview = MyPick<Todo, 'title' | 'completed'>
const todo: TodoPreview = {
title: 'Clean room',
completed: false,
}
// answer
type MyPick<T, K extends keyof T> = {
[P in K]: T[P]
}
实现一个 Pick 类型，用途是将原有类型的部分内容映射到新类型中
知识点：
extends
keyofin
2. Readonly
// answer
type MyReadonly<T> = {
readonly [K in keyof T]: T[K]
}
实现一个 Readonly 类型，保证属性均是只读
3. Tuple to Object
const tuple = ['tesla', 'model 3', 'model X', 'model Y'] as const
type result = TupleToObject<typeof tuple> // expected { tesla: 'tesla', 'model 3': 'model 3', 'model X': 'model X', 'model Y': 'model Y'}
// answer
type TupleToObject<T extends ReadonlyArray<string | number>> = {
[K in T[number]]: K
}
知识点：
as const数组和元组区别ReadonlyArrayT[number]
4. First of Array
type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]
type head1 = First<arr1> // expected to be 'a'
type head2 = First<arr2> // expected to be 3
// answer
type First<T extends any[]> = T[number] extends never ? never : T[0]
知识点：
never?
5. Length of Tuple
type tesla = ['tesla', 'model 3', 'model X', 'model Y']
type spaceX = ['FALCON 9', 'FALCON HEAVY', 'DRAGON', 'STARSHIP', 'HUMAN SPACEFLIGHT']
type teslaLength = Length<tesla> // expected 4
type spaceXLength = Length<spaceX> // expected 5
// answer
type Length<T extends readonly any[]> = T['length']
知识点：
length
6. Exclude
type Result = MyExclude<'a' | 'b' | 'c', 'a'> // 'b' | 'c'
// answer
知识点：
Exclude