1:动态添加 对象属性

var obj = new Object();

console.log (obj.username);

obj.username = "haha";

console.log (obj.username);

//undefined

//haha

用“[]”表示。写成 obj["username"] = "haha";

 var obj = new Object();

console.log (obj.username);

obj["username"] = "haha";

console.log (obj.username);

//undefined

//haha

还可以直接定义

var obj = {username:"haha", password:"123"};

console.log(obj.username);

console.log(obj.password);

//haha

//123

2:删除属性,使用 delete

var obj = new Object();

obj["username"] = "haha";

console.log (obj.username);

delete obj.username;

console.log (obj.username);

//haha

//undefined

3:修改原属性，增加新属性

var json = {  

    "age":24,  

    "name":"haha"  

};  

//修改Json中的age值

json["age"] = 30;  

console.log(json.age);

//30

//增加Json中的sex值

json["sex"] = "w";  

console.log(json.sex);

//w

4:Json对象与Json字符串互转

JSON.parse(jsonstr); //可以将json字符串转换成json对象

var jsObj = {}; 
jsObj.testArray = [1,2,3]; 
jsObj.name = 'CSS3'; 
jsObj.date = '2017'; 
console.log(jsObj) 
console.log(typeof(jsObj));
var str = JSON.stringify(jsObj); 
var str1 = JSON.parse(str); 
console.log(str) 
console.log(typeof(str)); 
console.log(str1) 
console.log(typeof(str1));
//Object {testArray: Array[3], name: "CSS3", date: "2017"}
//object
// {"testArray":[1,2,3],"name":"CSS3","date":"2017"}
// string
//Object {testArray: Array[3], name: "CSS3", date: "2017"}
// object

JSON.stringify(jsonobj); //可以将json对象转换成json字符串 

var jsObj = {}; 
jsObj.testArray = [1,2,3]; 
jsObj.name = 'CSS3'; 
jsObj.date = '2017'; 
console.log(jsObj) 
console.log(typeof(jsObj));
var str = JSON.stringify(jsObj); 
console.log(str) 
console.log(typeof(str));
//Object {testArray: Array[3], name: "CSS3", date: "2017"}
// object
// {"testArray":[1,2,3],"name":"CSS3","date":"2017"}

//string

转自：http://www.cnblogs.com/kelly2017/p/7074668.html