var xiaoming = {
    name: '小明',
    birth: 1990,
    school: 'No.1 Middle School',
    height: 1.70,
    weight: 65,
    score: null
};

注意最后一个键值没有,

xiaoming.name; // '小明'
xiaoming.birth; // 1990

属性名包含特殊字符

只能使用['xxx']来访问

var xiaohong = {
    name: '小红',
    'middle-school': 'No.1 Middle School'
};

xiaohong['middle-school']; // 'No.1 Middle School'
xiaohong['name']; // '小红'
xiaohong.name; // '小红'

访问不存在的属性返回undefined

var xiaoming = {
    name: '小明'
};
xiaoming.age; // undefined

JavaScript的对象是动态类型

自由地给一个对象添加或删除属性

var xiaoming = {
    name: '小明'
};
xiaoming.age; // undefined
xiaoming.age = 18; // 新增一个age属性
xiaoming.age; // 18
delete xiaoming.age; // 删除age属性
xiaoming.age; // undefined
delete xiaoming['name']; // 删除name属性
xiaoming.name; // undefined
delete xiaoming.school; // 删除一个不存在的school属性也不会报错

检测对象是否拥有某一属性

in

var xiaoming = {
    name: '小明',
    birth: 1990,
    school: 'No.1 Middle School',
    height: 1.70,
    weight: 65,
    score: null
};
'name' in xiaoming; // true
'grade' in xiaoming; // false

'toString' in xiaoming; // true 继承的

判断属性是自身拥有的，还是继承得到的

var xiaoming = {
    name: '小明'
};
xiaoming.hasOwnProperty('name'); // true
xiaoming.hasOwnProperty('toString'); // false