JS-对象数据属性

    var person = {};
    Object.defineProperty(person, "name", {
        writable: false, // 对象的数据属性不可写-类似常量
        value: "Nicholas"
    });
    console.log(person.name); // Nicholas
    person.name = "Michael";  // 重写对象的属性，无效
    delete person.name;       // 删除也是无效的
    console.log(person.name); // Nicholas

    var person = {};
    Object.defineProperty(person, "name", {
        // 不可配置 - 即不能再调用 Object.defineProperty 来修改
        configurable: false,
        value: "Nicholas"
    });
    //throws error
    Object.defineProperty(person, "name", {
        configurable: true,
        value: "Nicholas"
    });

属性描述符

    var book = {};
    Object.defineProperties(book, {
        _year: {value: 2004},
        edition: {value: 1},
        year: {            
            get: function(){
                return this._year;
            },
            set: function(newValue){
                if (newValue > 2004) {
                    this._year = newValue;
                    this.edition += newValue - 2004;
                }                  
            }            
        }        
    });
    // 获取对象的属性描述符
    var descriptor = Object.getOwnPropertyDescriptor(book, "_year");
    alert(descriptor.value);          //2004
    alert(descriptor.configurable);   //false
    alert(typeof descriptor.get);     //"undefined"
    var descriptor = Object.getOwnPropertyDescriptor(book, "year");
    alert(descriptor.value);          //undefined
    alert(descriptor.enumerable);     //false
    alert(typeof descriptor.get);     //"function"