TypeScript 体操

# Hello World

template

// type HelloWorld = number  // 下面Equal的判断为string 现为 number是错误的
type HelloWorld = string 

test

import type { Equal, Expect, NotAny } from '@type-challenges/utils'

type cases = [
  Expect<NotAny<HelloWorld>>,
  Expect<Equal<HelloWorld, string>>,
]

# Pick

template

// 类型约束 extends   keyof 遍历
type MyPick<T, K extends keyof T> = {
  [P in K]: T[P];
}
function myPick (todo, keys) {
  const obj = {}
  keys.forEach(key => {
    if (key in todo) {
      obj[key] = todo[key]
    }
  });
  return obj;
}
// 1. 返回一个对象
// 2. 遍历forEach
// 3. todo[key] 取值
// 4. 看看key 在不在 todo 里面

// function getPrototype <T, K>(obj: T, key: K) {
function getPrototype <T, K extends keyof T>(obj: T, key: K) {
  return obj[key]
}

test

import type { Equal, Expect } from '@type-challenges/utils'
type cases = [
  Expect<Equal<Expected1, MyPick<Todo, 'title'>>>,
  Expect<Equal<Expected2, MyPick<Todo, 'title' | 'completed'>>>,
  // @ts-expect-error
  MyPick<Todo, 'title' | 'completed' | 'invalid'>,
  
]

interface Todo {
  title: string
  description: string
  completed: boolean
}

interface Expected1 {
  title: string
}

interface Expected2 {
  title: string
  completed: boolean
}