iterator

<script>

    //通过for  of 实际值 /  for  in 下标
    var arr = [3,4,5]
    for (var x of arr){
        console.log(x)
    }

    var map = new Map([['tom',100],['jack',90],['haha',80]]);
    for (let x of map ){
        console.log(x)
    }
</script>