js遍历数组和对象的方法

https://www.cnblogs.com/yangshifu/p/7377102.html#for-of
https://www.cnblogs.com/lvmh/p/6104397.html
第二条链接里有分析不同遍历方式的效率

 var arr = ["name","age","sex"];
        var obj ={
            name: "gong",
            sex: "male",
            age: 18,
            hobby:function(){
                console.log("play footbale")
            }
        }
``
        // for-in遍历数组和和对象
        for(key in obj){
            console.log("key:"+key);//name sex age hobby
            console.log("value:" + obj[key]);//gong male 18 footable
        }

        //forEach遍历数组，三个参数依次是数组元素、索引、数组本身
        arr.forEach(function(value,index,array){
            console.log("arr:"+value+" "+index + array);
        })

        //Object.keys()返回一个数组
        let arr2 = Object.keys(arr);
        console.log("arr2:"+arr2)//(0,1,2)数组的索引组成的数组对象；
        let arr3 = Object.keys(obj);
        console.log("arr3:"+arr3);//(name,sex,age,hobby)//对象的属性名
        组成的数组对象；