定义多个属性 Object.defineProperties()

var book = {}
Object.defineProperties(book,{
    _year:{
        value:2004
    },
    editable:{
        value:1
    },
    year:{
    get:function(){
        return this._year
    },
    set:function(newYear){
        if(newYear > 2004){
            this._year = newYear;
            this.editable += newYear - 2004;
        }
    }
}})

// _year数据属性，year访问器属性