1果漾、實(shí)現(xiàn)一個(gè)call函數(shù)

// 思路：將要改變this指向的方法掛到目標(biāo)this上執(zhí)行并返回
Function.prototype.mycall = function (context) {
  if (typeof this !== 'function') {
    throw new TypeError('not funciton')
  }
  context = context || window
  context.fn = this
  let arg = [...arguments].slice(1)
  let result = context.fn(...arg)
  delete context.fn
  return result
} 

2、實(shí)現(xiàn)一個(gè)apply函數(shù)

// 思路：將要改變this指向的方法掛到目標(biāo)this上執(zhí)行并返回
Function.prototype.myapply = function (context) {
  if (typeof this !== 'function') {
    throw new TypeError('not funciton')
  }
  context = context || window
  context.fn = this
  let result
  if (arguments[1]) {
    result = context.fn(...arguments[1])
  } else {
    result = context.fn()
  }
  delete context.fn
  return result
}

3勾徽、實(shí)現(xiàn)一個(gè)bind函數(shù)

// 思路：類似call，但返回的是函數(shù)
Function.prototype.mybind = function (context) {
  if (typeof this !== 'function') {
    throw new TypeError('Error')
  }
  let _this = this
  let arg = [...arguments].slice(1)
  return function F() {
    // 處理函數(shù)使用new的情況
    if (this instanceof F) {
      return new _this(...arg, ...arguments)
    } else {
      return _this.apply(context, arg.concat(...arguments))
    }
  }
}

4统扳、instanceof的原理

// 思路：右邊變量的原型存在于左邊變量的原型鏈上
function instanceOf(left, right) {
  let leftValue = left.__proto__
  let rightValue = right.prototype
  while (true) {
    if (leftValue === null) {
      return false
    }
    if (leftValue === rightValue) {
      return true
    }
    leftValue = leftValue.__proto__
  }
}

5喘帚、Object.create的基本實(shí)現(xiàn)原理

// 思路：將傳入的對象作為原型
function create(obj) {
  function F() {}
  F.prototype = obj
  return new F()
}

6畅姊、new本質(zhì)
創(chuàng)建一個(gè)空的對象
讓構(gòu)造函數(shù)中的this指向這個(gè)空對象
根據(jù)構(gòu)造函數(shù)中的內(nèi)容，一次對空對象進(jìn)行賦值
返回我們所創(chuàng)建的對象
需要注意的是吹由，當(dāng)構(gòu)造函數(shù)返回值是一個(gè)對象是若未，我們使用new調(diào)用該構(gòu)造函數(shù)所生成的對象是構(gòu)造函數(shù)所返回的那個(gè)對象，當(dāng)構(gòu)造函數(shù)返回值為基本數(shù)據(jù)類型倾鲫，或者沒有返回值時(shí)粗合，則會將函數(shù)中聲明的屬性和方法添加在new所創(chuàng)建的新對象進(jìn)行返回

function myNew (fun) {
  return function () {
    // 創(chuàng)建一個(gè)新對象且將其隱式原型指向構(gòu)造函數(shù)原型
    let obj = {
      __proto__ : fun.prototype
    }
    // 執(zhí)行構(gòu)造函數(shù)
    fun.call(obj, ...arguments)
    // 返回該對象
    return obj
  }
}

function person(name, age) {
  this.name = name
  this.age = age
}
let obj = myNew(person)('chen', 18) // {name: "chen", age: 18}

7、實(shí)現(xiàn)一個(gè)基本的Promise

// 未添加異步處理等其他邊界情況
// ①自動執(zhí)行函數(shù)乌昔，②三個(gè)狀態(tài)隙疚，③then
class Promise {
  constructor (fn) {
    // 三個(gè)狀態(tài)
    this.state = 'pending'
    this.value = undefined
    this.reason = undefined
    let resolve = value => {
      if (this.state === 'pending') {
        this.state = 'fulfilled'
        this.value = value
      }
    }
    let reject = value => {
      if (this.state === 'pending') {
        this.state = 'rejected'
        this.reason = value
      }
    }
    // 自動執(zhí)行函數(shù)
    try {
      fn(resolve, reject)
    } catch (e) {
      reject(e)
    }
  }
  // then
  then(onFulfilled, onRejected) {
    switch (this.state) {
      case 'fulfilled':
        onFulfilled()
        break
      case 'rejected':
        onRejected()
        break
      default:
    }
  }
}

8、實(shí)現(xiàn)淺拷貝

// 1. ...實(shí)現(xiàn)
let copy1 = {...{x:1}}

// 2. Object.assign實(shí)現(xiàn)

let copy2 = Object.assign({}, {x:1})

9磕道、實(shí)現(xiàn)一個(gè)基本的深拷貝

// 1. JOSN.stringify()/JSON.parse()
let obj = {a: 1, b: {x: 3}}
JSON.parse(JSON.stringify(obj))

// 2. 遞歸拷貝
function deepClone(obj) {
  let copy = obj instanceof Array ? [] : {}
  for (let i in obj) {
    if (obj.hasOwnProperty(i)) {
      copy[i] = typeof obj[i] === 'object' ? deepClone(obj[i]) : obj[i]
    }
  }
  return copy
}

10供屉、使用setTimeout模擬setInterval

// 可避免setInterval因執(zhí)行時(shí)間導(dǎo)致的間隔執(zhí)行時(shí)間不一致
setTimeout (function () {
  // do something
  setTimeout (arguments.callee, 500)
}, 500)

11、js實(shí)現(xiàn)一個(gè)繼承方法// 借用構(gòu)造函數(shù)繼承實(shí)例屬性

// 借用構(gòu)造函數(shù)繼承實(shí)例屬性
function Child () {
  Parent.call(this)
}
// 寄生繼承原型屬性
(function () {
  let Super = function () {}
  Super.prototype = Parent.prototype
  Child.prototype = new Super()
})()

12溺蕉、實(shí)現(xiàn)一個(gè)基本的Event Bus

// 組件通信伶丐，一個(gè)觸發(fā)與監(jiān)聽的過程
class EventEmitter {
  constructor () {
    // 存儲事件
    this.events = this.events || new Map()
  }
  // 監(jiān)聽事件
  addListener (type, fn) {
    if (!this.events.get(type)) {
      this.events.set(type, fn)
    }
  }
  // 觸發(fā)事件
  emit (type) {
    let handle = this.events.get(type)
    handle.apply(this, [...arguments].slice(1))
  }
}

// 測試
let emitter = new EventEmitter()
// 監(jiān)聽事件
emitter.addListener('ages', age => {
  console.log(age)
})
// 觸發(fā)事件
emitter.emit('ages', 18)  // 18

13、實(shí)現(xiàn)一個(gè)雙向數(shù)據(jù)綁定

let obj = {}
let input = document.getElementById('input')
let span = document.getElementById('span')
// 數(shù)據(jù)劫持
Object.defineProperty(obj, 'text', {
  configurable: true,
  enumerable: true,
  get() {
    console.log('獲取數(shù)據(jù)了')
  },
  set(newVal) {
    console.log('數(shù)據(jù)更新了')
    input.value = newVal
    span.innerHTML = newVal
  }
})
// 輸入監(jiān)聽
input.addEventListener('keyup', function(e) {
  obj.text = e.target.value
})

完整實(shí)現(xiàn)可前往之前寫的：這應(yīng)該是最詳細(xì)的響應(yīng)式系統(tǒng)講解了
https://juejin.im/post/5d26e368e51d4577407b1dd7

14疯特、實(shí)現(xiàn)一個(gè)簡單路由

// hash路由
class Route{
  constructor(){
    // 路由存儲對象
    this.routes = {}
    // 當(dāng)前hash
    this.currentHash = ''
    // 綁定this哗魂，避免監(jiān)聽時(shí)this指向改變
    this.freshRoute = this.freshRoute.bind(this)
    // 監(jiān)聽
    window.addEventListener('load', this.freshRoute, false)
    window.addEventListener('hashchange', this.freshRoute, false)
  }
  // 存儲
  storeRoute (path, cb) {
    this.routes[path] = cb || function () {}
  }
  // 更新
  freshRoute () {
    this.currentHash = location.hash.slice(1) || '/'
    this.routes[this.currentHash]()
  }   
}

15、實(shí)現(xiàn)懶加載

<ul>
  <li><img src="./imgs/default.png" data="./imgs/1.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/2.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/3.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/4.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/5.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/6.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/7.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/8.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/9.png" alt=""></li>
  <li><img src="./imgs/default.png" data="./imgs/10.png" alt=""></li>
</ul>


let imgs =  document.querySelectorAll('img')
// 可視區(qū)高度
let clientHeight = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight
function lazyLoad () {
  // 滾動卷去的高度
  let scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop
  for (let i = 0; i < imgs.length; i ++) {
    // 圖片在可視區(qū)冒出的高度
    let x = clientHeight + scrollTop - imgs[i].offsetTop
    // 圖片在可視區(qū)內(nèi)
    if (x > 0 && x < clientHeight+imgs[i].height) {
      imgs[i].src = imgs[i].getAttribute('data')
    } 
  }      
}
// addEventListener('scroll', lazyLoad) or setInterval(lazyLoad, 1000)

16辙芍、rem實(shí)現(xiàn)原理

// 原始配置
function setRem () {
  let doc = document.documentElement
  let width = doc.getBoundingClientRect().width
  let rem = width / 75
  doc.style.fontSize = rem + 'px'
}
// 監(jiān)聽窗口變化
addEventListener("resize", setRem)

17啡彬、手寫實(shí)現(xiàn)AJAX

// 1. 簡單流程

// 實(shí)例化
let xhr = new XMLHttpRequest()
// 初始化
xhr.open(method, url, async)
// 發(fā)送請求
xhr.send(data)
// 設(shè)置狀態(tài)變化回調(diào)處理請求結(jié)果
xhr.onreadystatechange = () => {
  if (xhr.readyStatus === 4 && xhr.status === 200) {
    console.log(xhr.responseText)
  }
}

// 2. 基于promise實(shí)現(xiàn) 

function ajax (options) {
  // 請求地址
  const url = options.url
  // 請求方法
  const method = options.method.toLocaleLowerCase() || 'get'
  // 默認(rèn)為異步true
  const async = options.async
  // 請求參數(shù)
  const data = options.data
  // 實(shí)例化
  const xhr = new XMLHttpRequest()
  // 請求超時(shí)
  if (options.timeout && options.timeout > 0) {
    xhr.timeout = options.timeout
  }
  // 返回一個(gè)Promise實(shí)例
  return new Promise ((resolve, reject) => {
    xhr.ontimeout = () => reject && reject('請求超時(shí)')
    // 監(jiān)聽狀態(tài)變化回調(diào)
    xhr.onreadystatechange = () => {
      if (xhr.readyState == 4) {
        // 200-300 之間表示請求成功，304資源未變故硅，取緩存
        if (xhr.status >= 200 && xhr.status < 300 || xhr.status == 304) {
          resolve && resolve(xhr.responseText)
        } else {
          reject && reject()
        }
      }
    }
    // 錯(cuò)誤回調(diào)
    xhr.onerror = err => reject && reject(err)
    let paramArr = []
    let encodeData
    // 處理請求參數(shù)
    if (data instanceof Object) {
      for (let key in data) {
        // 參數(shù)拼接需要通過 encodeURIComponent 進(jìn)行編碼
        paramArr.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]))
      }
      encodeData = paramArr.join('&')
    }
    // get請求拼接參數(shù)
    if (method === 'get') {
      // 檢測url中是否已存在 ? 及其位置
      const index = url.indexOf('?')
      if (index === -1) url += '?'
      else if (index !== url.length -1) url += '&'
      // 拼接url
      url += encodeData
    }
    // 初始化
    xhr.open(method, url, async)
    // 發(fā)送請求
    if (method === 'get') xhr.send(null)
    else {
      // post 方式需要設(shè)置請求頭
      xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded;charset=UTF-8')
      xhr.send(encodeData)
    }
  })
}

18庶灿、實(shí)現(xiàn)拖拽

window.onload = function () {
  // drag處于絕對定位狀態(tài)
  let drag = document.getElementById('box')
  drag.onmousedown = function(e) {
    var e = e || window.event
    // 鼠標(biāo)與拖拽元素邊界的距離 = 鼠標(biāo)與可視區(qū)邊界的距離 - 拖拽元素與邊界的距離
    let diffX = e.clientX - drag.offsetLeft
    let diffY = e.clientY - drag.offsetTop
    drag.onmousemove = function (e) {
      // 拖拽元素移動的距離 = 鼠標(biāo)與可視區(qū)邊界的距離 - 鼠標(biāo)與拖拽元素邊界的距離
      let left = e.clientX - diffX
      let top = e.clientY - diffY
      // 避免拖拽出可視區(qū)
      if (left < 0) {
        left = 0
      } else if (left > window.innerWidth - drag.offsetWidth) {
        left = window.innerWidth - drag.offsetWidth
      }
      if (top < 0) {
        top = 0
      } else if (top > window.innerHeight - drag.offsetHeight) {
        top = window.innerHeight - drag.offsetHeight
      }
      drag.style.left = left + 'px'
      drag.style.top = top + 'px'
    }
    drag.onmouseup = function (e) {
      this.onmousemove = null
      this.onmouseup = null
    }
  }
}

19、實(shí)現(xiàn)一個(gè)節(jié)流函數(shù)

// 思路：在規(guī)定時(shí)間內(nèi)只觸發(fā)一次
function throttle (fn, delay) {
  // 利用閉包保存時(shí)間
  let prev = Date.now()
  return function () {
    let context = this
    let arg = arguments
    let now = Date.now()
    if (now - prev >= delay) {
      fn.apply(context, arg)
      prev = Date.now()
    }
  }
}

function fn () {
  console.log('節(jié)流')
}
addEventListener('scroll', throttle(fn, 1000)) 

20吃衅、實(shí)現(xiàn)一個(gè)防抖函數(shù)

// 思路:在規(guī)定時(shí)間內(nèi)未觸發(fā)第二次往踢，則執(zhí)行
function debounce (fn, delay) {
  // 利用閉包保存定時(shí)器
  let timer = null
  return function () {
    let context = this
    let arg = arguments
    // 在規(guī)定時(shí)間內(nèi)再次觸發(fā)會先清除定時(shí)器后再重設(shè)定時(shí)器
    clearTimeout(timer)
    timer = setTimeout(function () {
      fn.apply(context, arg)
    }, delay)
  }
}

function fn () {
  console.log('防抖')
}
addEventListener('scroll', debounce(fn, 1000))