操作对象

删除一个对象的key值
方法1：
var data={
       province:'',
       city:''
}
delete(data["province"]);
console.log(data)//data={city:''}
方法2：
var data={
       province:'',
       city:''
}
delete data.province
console.log(data)//data={city:''}

判断对象是否存在
1、JSON.stringify(要判断的对象)==="{}"   h5
2、Object.keys(要判断的对象).length===0  h5   ES6的新方法
3、var keys=[]
  for(var key in {要判断的对象}){
     keys.push(key)
  }
  keys  = =[] ??
  var keys=[]
  for(var key in {a:1,d:2}){
     keys.push(key)
  }
  keys  = =["a","b"]
4、jquery的isEmptyObject方法
var data = {}
var b = $.isEmptyObject(data);
alert(b);//true
5、Object.getOwnPropertyNames()方法
var data ={};
var arr = Object.getOwnPropertyNames(data);
alert(arr.length==0);//true  不兼容IE8