map，reduce，filter使用

<script>
    var arr = [
        {
            age:11,
            name:'aa'
        },
        {
            age:22,
            name:'bb'
        },
        {
            age:33,
            name:'cc'
        }
    ]
    // map 使用
    var age = arr.map((item,index)=>{
        console.log(item,index)  //数组项，下标
        return item.age
    })  
    console.log(age) //  [11, 22, 33]
    // es6写法
    var ageEs6 = arr.map(item=>item.age)
    console.log(ageEs6) //  [11, 22, 33]

    // reduce
    // 累加计算
    var ageR = arr.reduce((n,y)=>{
        console.log(n, y, y.age) // n:初始值  y:循环项
        return n + y.age
    },0)  //第二个参数定义初始值
    console.log(ageR) //0 + 11 + 22 + 33 = 66 获取最终结果

    // es6写法
    var ageRes6 = arr.reduce((n,y)=> n + y.age, 0)
    console.log(ageRes6) //66
　　
　　案例：合并数组对象里的子数组
　　

var arr = [
        {
            title:'11',
            arrChild:[
                {
                    name:'a',
                    age:12
                }
            ]
        },
        {
            title:'22',
            arrChild:[
                {
                    name:'b',
                    age:12
                }
            ]
        },
        {
            title:'33',
            arrChild:[
                {
                    name:'c',
                    age:12
                }
            ]
        },
        
    ]

    let newArr = arr.reduce((a,b)=>
        a.concat(b.arrChild)
    ,[])
    console.log(newArr);////[{name: "a", age: 12},{name: "b", age: 12},{name: "b", age: 12}]

    // filter 过滤
    var arrName = arr.filter((item)=>{
        return item.name == 'cc'
    })

    var arrName2 = arr.filter(item=> item.name == 'cc')
    console.log(arrName,arrName2) // [ {age:33,name:'cc'} ] 

    var arrAge = arr.filter(item=> item.age > 20)
    console.log(arrAge) 

</script>