常见手写代码题——面试官养成计划

1.防抖：

function debounce(fn, delay) {
  let timer
  return function (...args) {
    if (timer) {
      clearTimeout(timer)
    }
    timer = setTimeout(() => {
      fn.apply(this, args)
    }, delay)
  }
}

// 测试
const task = () => {
  console.log('run task')
}
const debounceTask = debounce(task, 1000)
window.addEventListener('scroll', debounceTask)

2.节流

function throttle(fn, delay) {
  let last = 0 // 上次触发时间
  return (...args) => {
    const now = Date.now()
    if (now - last > delay) {
      last = now
      fn.apply(this, args)
    }
  }
}

// 测试
const task = () => {
  console.log('run task')
}
const throttleTask = throttle(task, 1000)
window.addEventListener('scroll', throttleTask)

3.深拷贝

function deepClone(obj, cache = new WeakMap()) {
  if (typeof obj !== 'object') return obj // 普通类型，直接返回
  if (obj === null) return obj
  if (cache.get(obj)) return cache.get(obj) // 防止循环引用，程序进入死循环
  if (obj instanceof Date) return new Date(obj)
  if (obj instanceof RegExp) return new RegExp(obj)
  
  // 找到所属原型上的constructor，所属原型上的constructor指向当前对象的构造函数
  let cloneObj = new obj.constructor()
  cache.set(obj, cloneObj) // 缓存拷贝的对象，用于处理循环引用的情况
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      cloneObj[key] = deepClone(obj[key], cache) // 递归拷贝
    }
  }
  return cloneObj
}

// 测试
const obj = { name: 'Jack', address: { x: 100, y: 200 } }
obj.a = obj // 循环引用
const newObj = deepClone(obj)
console.log(newObj.address === obj.address) // false

4.实现Promise

class MyPromise {
  constructor(executor) { // executor执行器
    this.status = 'pending' // 等待状态
    this.value = null // 成功或失败的参数
    this.fulfilledCallbacks = [] // 成功的函数队列
    this.rejectedCallbacks = [] // 失败的函数队列
    const that = this
    function resolve(value) { // 成功的方法
      if (that.status === 'pending') {
        that.status = 'resolved'
        that.value = value
        that.fulfilledCallbacks.forEach(myFn => myFn(that.value)) //执行回调方法
      }
    }
    function reject(value) { //失败的方法
      if (that.status === 'pending') {
        that.status = 'rejected'
        that.value = value
        that.rejectedCallbacks.forEach(myFn => myFn(that.value)) //执行回调方法
      }
    }
    try {
      executor(resolve, reject)
    } catch (err) {
      reject(err)
    }
  }
  then(onFulfilled, onRejected) {
    if (this.status === 'pending') {
      // 等待状态，添加回调函数到成功的函数队列
      this.fulfilledCallbacks.push(() => {
        onFulfilled(this.value)
      })
      // 等待状态，添加回调函数到失败的函数队列
      this.rejectedCallbacks.push(() => {
        onRejected(this.value)
      })
    }
    if (this.status === 'resolved') { // 支持同步调用
      console.log('this', this)
      onFulfilled(this.value)
    }
    if (this.status === 'rejected') { // 支持同步调用
      onRejected(