数组去重的常用方法，利用Promise实现函数按序执行

    //普通数组去重

    let ary = [1,2,3,1,2,3,1,2,3]

    //方法一  for循环+三目运算
    Array.prototype.quchong1 = function (){
        let obj = {}
        let result = []
        for(let i = 0; i< this.length; i++){
            obj[this[i]] ?  '' : ( obj[this[i]] = result.push(this[i]) )
        }
        return result
    }
    console.log(ary.quchong1())  // [1, 2, 3]


    // 方法二 过滤filter
    Array.prototype.quchong2 = function () {
        let result = this.filter(
            (item,index,self) => {
                return self.indexOf(item) === index
            }
        )
        return result
    }
    console.log(ary.quchong2()) //[1, 2, 3]


    //方法三 reduce + 短路或
    Array.prototype.quchong3 = function () {
        let obj = {}
        let result = this.reduce(
            (pre,cur,index)=>{
                obj[cur] || (obj[cur] = pre.push(cur))
                return pre
            },[]
        )
        return result
    }
    console.log(ary.quchong3())


    //方法四 new Set  + 扩展运算符...
    Array.prototype.quchong4 = function () {
        let result = [...new Set(this)]
        return result
    }
    console.log(ary.quchong4()) //[1, 2, 3]

    // 对数组中相同的对象进行去重
    let ary2 = [
        {name: 'zh'},
        {name: 'zh'},
        {name: 'yy'},
        {name: 'zh'}
    ]
    
    //方法一 for循环 + 三目运算
    Array.prototype.quchong5 = function () {
        let obj = {}
        let result = []
        for ( let i =0; i < ary2.length; i++ ) {
            obj[this[i].name]  ?  '' :  obj[this[i].name] = result.push(this[i])
        }
        return result
    }
    console.log(ary2.quchong5()) //[ {name: 'zh'},{name: 'yy'}]

    
    
    //方法二 for循环 + 短路或
    Array.prototype.quchong6 = function () {
        let obj = {}
        let result = []
        for ( let i =0; i < ary2.length; i++ ) {
            obj[this[i].name] || ( obj[this[i].name] = result.push(this[i]) )
        }
        return result
    }
    console.log(ary2.quchong6()) //[ {name: 'zh'},{name: 'yy'}]

    
    
    //方法三 reduce + 短路或
    Array.prototype.quchong7 = function (){
        let obj = {}
        let result = this.reduce(
            (pre,cur,index) => {
                obj[cur.name] || ( obj[cur.name] = pre.push(cur) )
                return pre
            },[]
        )
        return result
    }
    console.log(ary2.quchong7()) //[ {name: 'zh'},{name: 'yy'}]

 利用Promise实现函数按序执行

  function a () {
      setTimeout(
          ()=>{ console.log(1)},3000
      )
  }
  function b () {
      setTimeout(
          ()=>{ console.log(2)},2000
      )
  }
  function c () {
      setTimeout(
          ()=>{ console.log(3)},1000
      )
  }
  a()
  b()
  c()
//  执行输出结果为 3 2 1

 // 利用promise 实现 函数按序执行
function a () {
    return new Promise(
        (resolve,reject) => {
            setTimeout(
                ()=>{
                    console.log(1)
                    resolve()
                },3000
            )
        }
    )
}
function b () {
    return new Promise(
        (resolve,reject) => {
            setTimeout(
                ()=>{
                    console.log(2)
                    resolve()
                },2000
            )
        }
    )
}
function c () {
    return new Promise(
        (resolve,reject) => {
            setTimeout(
                ()=>{
                    console.log(3)
                    resolve()
                },1000
            )
        }
    )
}


//  方法一
a().then(b).then(c) //执行结果 1 2 3


//  方法二
async function d () {
    await a()
    await b()
    await c()
}
d() //执行结果  1   2   3