Object.keys() 方法详解与实战应用

// 1. 定义一个对象
    var obj = { 0:'熊大',1:'熊二',2:'光头强' }
    // 2. 使用Object.keys()方法
    var keyValue = Object.keys(obj)
    // 3. 打印结果
    console.log(keyValue)  // 得到是：["0","1","2"]

var obj2 = {'name':'a','list':{'a':'value1','b':'value2'},'num':13}
var keyValue2 = Object.keys(obj2)
console.log(keyValue2)  // 得到是：["name","list","num"]

 Object.keys(obj2).forEach(function(key){
     console.log(key, obj2[key]);
     })
     // 得到的是：name---a
     //          list---{a:"value",b:"value"}
     //          num----13 

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Object.keys()处理对象，返回可枚举的属性数组</title>
    </head>
    <body>
        <script type="text/javascript">
            let person={
                name:'一只流浪的kk',
                age:20,
                eat:function(){}
            }
            console.log(Object.keys(person));//    ['name','age','eat']
        </script>
    </body>
</html>

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Object.keys()处理数组，返回索引值数组</title>
    </head>
    <body>
        <script type="text/javascript">
            let arr=[1,2,3,4,5];
            console.log(Object.keys(arr));//['0','1','2','3','4','5']
        </script>
    </body>
</html>

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Object.keys()处理字符串，返回索引值数组</title>
    </head>
    <body>
        <script type="text/javascript">
            let str='hello';
            console.log(Object.keys(str));//['0','1','2','3','4']
        </script>
    </body>
</html>

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
           let person={
                   name:'一只流浪的kk',
                   age:18,
                   eat:function(){
                   }
           }
           Object.keys(person).map((key)=>{
                   person[key];//获得属性对应的值，可以进行其它处理
           })
        </script>
    </body>
</html>

Object.keys("foo");
// TypeError: "foo" is not an object (ES5 code)
Object.keys("foo");
// ["0", "1", "2"]                   (ES2015 code)