javascript 对象属性的添加，删除，json对象和字符串转换方法等

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//1232:删除属性,使用 deletevar obj = new Object();obj["username"] = "haha";console.log (obj.username);delete obj.username;console.log (obj.username);//haha//undefined3: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);//w4: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