创建变量

// 创建变量
var car = "porsche";

创建对象

1、使用{}创建对象

// 创建对象：
var person = {firstName:"Bill", lastName:"Gates", age:62, eyeColor:"blue"};
var firstName = person.firstName;  // Bill

2、使用new创建对象

var person = new Object();
person.firstName = "Bill";
person.lastName = "Gates";
person.age = 50;
person.eyeColor = "blue"; 
var firstName  = person.firstName;  // Bill

3、使用构造器创建对象

// Person 对象的构造器函数
function Person(first, last, age, eye) {this.firstName = first;this.lastName = last;this.age = age;this.eyeColor = eye;
}// 创建 Person 对象
var myFriend = new Person("Bill", "Gates", 23, "blue");
var age = myFriend.age;  // 23

对象的参数值是易变的

//创建对象
var person = {firstName:"Bill", lastName:"Gates", age:23, eyeColor:"blue"}
//将该赋给x
var x = person;
x.age = 10;
//取值
var age = person.age;  // 10

访问对象

1、使用.property访问对象的属性

var person = {firstname:"Bill",lastname:"Gates",age:23,eyecolor:"blue"
};var firstname = person.firstname;   // Bill

2、使用 ["property"]访问对象的属性

var person = {firstname:"Bill",lastname:"Gates",age:23,eyecolor:"blue"
};var firstname = person["firstname"];   // Bill

 3、使用for in 访问对象的属性

var person = { fname: "Bill", lname: "Gates", age: 62 };
var x;
for (x in person) {console.log(x + "：" + person[x]);
}
// fname：Bill
// lname：Gates
// age：62

向对象中添加新属性

var person = {firstname:"Bill",lastname:"Gates",age:62,eyecolor:"blue"
};
//添加新属性
person.nationality = "English";
//访问新属性
var nationality  = person.nationality;   // English

删除对象中的属性

var person = {firstname:"Bill",lastname:"Gates",age:62,eyecolor:"blue"
};
//删除属性
delete person.age;
//打印对象
var x;
for (x in person) {console.log(x + "：" + person[x]);
}
//firstname：Bill
//lastname：Gates
//eyecolor：blue//打印已删除的属性
var age = person.age;    //不存在了，报错日志： Bill is undefined years old.

访问JSON对象

1、使用.property访问JSON对象的属性

var myObj = {"name":"Bill Gates", "age":23, "car":null};
var x = myObj.name;   // Bill Gates

2、使用 ["property"]访问JSON对象的属性

var myObj = {"name":"Bill Gates", "age":23, "car":null};
var x = myObj["name"];   // Bill Gates

 3、使用for in 访问JSON对象的属性

var myObj = {"name":"Bill Gates", "age":62, "car":null};
var x;
for (x in myObj) {console.log(x + "：" + myObj[x]);
}
//name：Bill Gates
//age：62
//car：null

4、访问嵌套的 JSON 对象的属性

var myObj = {"name":"Bill Gates","age":62,"cars": {"car1":"Porsche","car2":"BMW","car3":"Volvo"}
}
//使用.property访问
var car3 = myObj.cars.car3;   // Volvo
//使用 ["property"]访问
var car3 = myObj.cars["car3"];   // Volvo

修改JSON对象中属性的值

1、使用.property修改

var myObj = {"name": "Bill Gates","age": 23,"cars": {"car1": "Porsche","car2": "BMW","car3": "Volvo"}
}
myObj.cars.car2 = "Mercedes Benz";
var i;
for (i in myObj.cars) {console.log(i + ":" + myObj.cars[i]);
}
//car1:Porsche
//car2:Mercedes Benz
//car3:Volvo

2、使用 ["property"]修改

var myObj = {"name": "Bill Gates","age": 23,"cars": {"car1": "Porsche","car2": "BMW","car3": "Volvo"}
}
myObj.cars["car2"] = "Mercedes Benz";
var i;
for (i in myObj.cars) {console.log(i + ":" + myObj.cars[i]);
}
//car1:Porsche
//car2:Mercedes Benz
//car3:Volvo

删除JSON对象中属性

var myObj = {"name": "Bill Gates","age": 23,"cars": {"car1": "Porsche","car2": "BMW","car3": "Volvo"}
}
delete myObj.cars.car3;
var i;
for (i in myObj.cars) {console.log(i + ":" + myObj.cars[i]);
}
//car1:Porsche
//car2:Mercedes Benz