for循环
var arr = ["one","two","three",4,5,6];
for(var i = 0;i < arr.length;i++){
console.log(arr[i]);
}
//输出
one
two
three
4
5
6
for...in
var arr = ["one","two","three",4,5,6];
for(var item in arr){ //item是数组的下标，for...in循环的是key
console.log(arr[item]+"/"+item);
}
//输出
one/0
two/1
three/2
4/3
5/4
6/5
for...of
var arr = ["one","two","three",4,5,6];
for(var item of arr){ //item是定义的代表数组的变量，for...of循环的是value
console.log(item);
}
//输出
one
two
three
4
5
6
forEach方法
var arr = [4,5,6];
//ele为数组中的元素，index为数组的下标
var res = arr.forEach(function(ele,index,arr){
ele*10;
});
console.log(arr);
console.log(res); //--> undefined;
//输出
[Log] [40, 50, 60] (3) (forEach.html, line 17)
[Log] undefined (forEach.html, line 18)
ps:没有赋值的元素不会在forEach中循环迭代出,forEach没有return值，
map方法
var arr = [4,5,6];
//ele为数组中的元素，index为数组的下标
var res = arr.map(function(ele,index,arr){
return ele*10;
});
console.log(arr);
console.log(res);
//输出
[Log] [4, 5, 6] (3) (forEach.html, line 17)
[Log] [40, 50, 60] (3) (forEach.html, line 18)
ps:map有return值
