1、for in / for of

var array = [1,2,3,4,5];
for(let index in array)
{
    console.log(index, array[index]);
};

var obj = {a:1, b:2, c:"qqq"};
for(let index in obj)
{
    console.log(index, obj[index]);
};

for(let index of array){ 
    console.log(index)
}

註：for of 不支持對象，是直接得到值

for(let index in
 
 array){console.log(index, array[index]);};
0 1
1 2
2 3
3 4
4 5

for(let index of array){console.log(index, array[index]);};
1 2
2 3
3 4
4 5
5 undefined

2、forEach

var array = [1,2,3,4,5];
var num = null;
var result = array.forEach( a => 
{
    num += a; return a+1; 
});
> console.log(result);
undefined
 
> console.log(num)
1 15
> console.log(array)
(5) [1, 2, 3, 4, 5]

未完待續。。。

es6 遍歷總結