比如有一个数组

let arr = [

{name:'aaa',num:1},
{name:'aaa',num:2},
{name:'aaa',num:3},

{name:'bbb',num:4},
{name:'bbb',num:5},
{name:'bbb',num:6},

{name:'ccc',num:7},
{name:'ccc',num:8},
{name:'ccc',num:9}

]

我们希望得到  

[

　　{name:'aaa',sum:6},      //sum是所有num相加的值

　　{name:'bbb',sum:15},

　　{name:'bbb',sum:24},

]

//第一步，先给原数组分类，用reduce  

const result = arr.reduce((a,b)=>{
if(a[b.name]){    //根据name分类
a[b.name].push(b)
}else{
a[b.name] = [b]
}
return a
},{})

console.log(result)

//打印会得到  result 如下

{

　　aaa:[{name:'aaa',num:1},{name:'aaa',num:2},{name:'aaa',num:3}],

　　bbb:[{name:'bbb',num:4},{name:'bbb',num:5},{name:'bbb',num:6}],

　　ccc:[{name:'ccc',num:7},{name:'ccc',num:8},{name:'ccc',num:9}]

}

 

//我们操作result对象 

let resultArr = []           for (const key in result) {           let obj = {}        let sum= 0        result[key].forEach(item=>{                   sum += Number(item.num)                               }) 　　obj.name = result[key][0].name        obj.sum= sum        resultArr .push(obj) }
//打印resultArr 即可得到 console.log(resultArr )

[

　　{name:'aaa',sum:6},      

　　{name:'bbb',sum:15},

　　{name:'bbb',sum:24},

]