1. Array 转Map

// create array data
let arr = [
                {type:'1',name:'name1'},
                {type:'2',name:'name2'}
           ];
// convert array data to map
let map  = new Map(arr.map(i =>[i.type,i]));

2. Array reduce sum

// create array data
let arr = [
                {type:'1',count:1},
                {type:'2',count:2}
           ];
// sum count value
let sum  = reduce((accumulator, currentValue)=>accumulator+currentValue.count,0);

3. ES6 Array average

let average = array.reduce((sum,value)=>sum+value,initValue)/array.length

let arr = [{count:1,name:'test1'},{count:2,name:'test2'}];
let average = arr.reduce((sum,value)=>sum+value.count,0)/arr.length;