JS的数组遍历的常用方法实例

for(var i=0 , len= arr.length ; i<len ; i++){  代码块 }

var arr=[12,14,15,17,18];
var res=arr.forEach(function(item,index,input){
   input[index]=item*10;
});
console.log(res);     //undefined
console.log(arr);     //会对原来的数组产生改变

var arr=[12,14,15,17,18];
var res=arr.forEach(function(item,index,input){
   return item*10;
});
console.log(res);     //undefined
console.log(arr);     //[12,14,15,17,18]没变

var arr=[12,14,15,17,18];
var res=arr.map(function(item,index,input){
    return item*10;
});
console.log(res);    //[120,140,150,170,180]
console.log(arr);    //[12,14,15,17,18]

var arr=[12,14,15,17,18];
var res=arr.map(function(item,index,input){
   input[index]=item*10;
});
console.log(res);     //[undefined, undefined, undefined, undefined, undefined]
console.log(arr);     //[120,140,150,170,180]