js遍历数组和对象的方法

https://www.cnblogs.com/yangshifu/p/7377102.html#for-of
https://www.geek-share.com/detail/2691146661.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；