防抖 与 节流

function debounce(fn, timeout){
  var timers
  return function() {
    if (timers) {
      clearTimeout(timers)
    }
    let args = arguments;
    timers = setTimeout(() => {
      fn.apply(this, args)
    }, timeout)
  }
}

function throttle(fn, timeout) {
  var isCan = true
  return function() {
    if (!isCan) {
      return
    }
    isCan = false
    let args = arguments;
    setTimeout(()=>{
      fn.apply(this, args)
      isCan = true
    }, timeout)
  }
}

深拷贝

function deeCopy(obj) {
  if(typeof obj === 'object') {
    let newObj = Array.isArray(obj)?[]:{}
    for(let key in obj) {
      if(obj.hasOwnProperty(key)) {
        newObj[key] = deeCopy(obj[key])
      }
    }
    return newObj
  } else {
    return obj
  }
}

函数柯里化

function myCurrying() {
  let arg1 = Array.prototype.slice.call(arguments)
  let sum = eval(arg1.join('+'))
  function inner() {
    let arg2 = Array.prototype.slice.call(arguments)
    return myCurrying(sum+eval(arg2.join('+')))
  }
  // 若要省略后缀myval 可以试试toString (浏览器里可以直接出值)
  inner.myval = function () {
    return sum
  }
  return inner
}

// console.log(myCurrying(1, 2)(3)(1,5,9,8).myval())

// 或
function curry() {
  let args = [].slice.call(arguments)
  function inner() {
    let arg2 = [].slice.call(arguments)
    if (arg2.length==0) {
      return eval(args.join('+'))
    } else {
      return curry(eval(args.join('+')) + eval(arg2.join('+')))
    }
  }
  return inner
}

// console.log(curry(3,4)(2,5)())

数组reduce函数

Array.prototype.reduce = function (fn, base = 0) {
  for(let i=0,len=this.length;i<len;i++) {
    base = fn(base, this[i])
  }
  return base
}

let array = [1,2,1,3,4]

let result = array.reduce(function(pre, item){
  return pre+item
}, 9)
// console.log(result)

多维数组转一维数组

// 多维数组转一维
let arr = [1,2,3,[4,5,[6]]]

let newArr = JSON.stringify(arr).replace(/\[|\]/g, '').split(',').map(parseInt) // !!! [ 1, NaN, NaN, NaN, NaN, NaN ]

let newArr1 = arr.toString().split(',').map(Number) // [ 1, 2, 3, 4, 5, 6 ]

console.log(newArr)

// ES6
console.log(arr.flat(Infinity))

Promise all函数

Promise.all = function (pArr) {
  return new Promise((resolve, reject)=>{
    let result = [], count = 0
    if (pArr.length==0) {
      resolve(result)
    } else {
      for(let i=0,len=pArr.length;i<len;i++) {
        Promise.solve(pArr[i]).then((res)=>{
          result[i] = res
          count++
          if(count>=pArr.length) {
            resolve(result)
          }
        }, (error) => {
          reject(error)
        })
      }
    }
  })
}

js事件模型

class EventEmitter {
  constructor () {
    this._events = Object.create(null)
  }
  on(event, callback) {
    if(this._events[event]) {
      this._events[event].push(callback)
    } else {
      this._events[event] = [callback]
    }
  }
  off (event, callback) {
    if (this._events[event]) {
      let index = this._events[event].indexOf(callback)
      if(index>-1) {
        this._events[event].splice(index, 1)
      }
    }
  }
  emit(event) {
    let args = Array.prototype.slice.call(arguments, 1)
    for(let i=0,len=this._events[event].length;i<len;i++) {
      this._events[event][i].apply(this, args)
    }
  }
  once(event, callback) {
    let only = function(){
      callback.apply(this, arguments)
      this.off(event, only)
    }
    this.on(event, only)
  }
}

手写Ajax

function myAjax(type, url, data, callback) {
  let xhr = new XMLHttpRequest()
  xhr.open(type, url)
  if (type=='post') {
    xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded')
  }
  xhr.send(data)
  xhr.onreadystatechange = function () {
    if (xhr.readyState==4&&xhr.status==200) {
      callback(xhr.responseText)
    }
  }
}

实现jsonp

function myJsonp(url, callback) {

  var cbFuncName =  'my_json_cb_' + Math.random().toString().replace('.','');
  let script = document.createElement('script')
  script.src = url + '?callback=' + cbFuncName

  document.body.appendChild(script)

  window[cbFuncName] = function(data) {
    callback(data)
    document.body.removeChild(script)
  }
}

二叉树遍历

// 先序遍历（深度优先）递归法
function preOrder (node) {
  if (node==null) {
    return
  }
  console.log(node.val)
  preOrder(node.left)
  preOrder(node.right)
}

// 中序后序同理

链表反转

// 链表反转
function reverseLink (node) {
  let end = null, temp
  while(node!=null) {
    temp = node.next
    node.next = end

    end = node
    node = temp
  }
  return end
}