一、遍历对象

1、for-in遍历

    var obj = {a: 'ss', b: 'bb', c: 'cc'};
    for (var i in obj){
        console.log(i+':'+obj[i]);
    }

2、forEach遍历,先通过Object.keys()返回一个数组

    Object.keys(obj).forEach((value, index)=>{
        console.log(value, index,obj[value]);
    });
    //等同于
    Object.keys(obj).forEach(function (value, index,c) {
        console.log(value, index,obj[value]);
    });

3、jQuery的$.each()方法：它接受两个参数，分别指代属性名和属性值

    $.each(obj,function(key,value){
        console.log(key+": "+value)
    });

二、查看对象

      obj.a与obj['a']都能获取到

    console.log(obj.a);
    console.log(obj['a']);

三、删除对象

delete  obj[b];

四、判断对象是否为空

    delete obj.a;
    delete obj.b;
    console.log(obj, JSON.stringify(obj) === '{}');// { c: 'cc' } false
    console.log(obj, Object.keys(obj));           // { c: 'cc' } [ 'c' ]
    delete obj.c
    console.log(obj, JSON.stringify(obj) === '{}');// {} true
    console.log(obj, Object.keys(obj))             // {} []