es6 array operations (map, reduce, filter, foreach)

1. map map
2. reduce Summary
3. Filter filter
4. foreach loop (iteration)

map

let arr=[12,5,8];
let result=arr.map(function(item){
	return item*2;
});
alert(result);

reduce (out of a pile of data results)

        let arr=[12,69,180,8763];
        let result=arr.reduce(function(tmp, item,index){
          return tmp+item});
    //计算平均值

****

        let arr=[12,69,180,8763];
        let result=arr.reduce(function(tmp, item,index){
             if(index!=arr.length-1){
                 return tmp+item;}
            else{ 
                return (tmp+item)/arr.length;}
              );

tmp: intermediate result
item: an array of current position
index: the number of iterations

filter

let arr=[72,5,8,99,10,36];
let result=arr.filter(item=>(
    if(item%3==0){
    return true;
    }else{
    return false;
    }
));

// 72,99,36 output
equivalent to

let result=arr.filter(item=>{
	return item%3==0;
});

foreach

let arr=[12,5,8,9];
arr.foreach(item=>{
	alert(index+':'+item);
});