实例详解-类（二）

 

//===给Object.prototype添加只读\不可枚举\不可配置的属性objectId
(function(){
    Object.defineProperty(Object.prototype,'objectId',{
        get:idGetter,      //读取objectId时直接调用idGetter函数
        enumerable:false,
        configurable:false
    });
    function idGetter(){
        if(!(idprop in this)) {   //检测是否存在idprop
            if (!Object.isExtensible(this)) {
                throw Error('can not define id for nonextensible objects');
            }
            Object.defineProperty(this, idprop, {
                value: nextid++,
                writable: false,
                enumerable: false,
                configurable: false
            });
        }
        return this(idprop);
    }
    var idprop = '|**objectid**|'; //假设这个属性没用到
    var nextid = 1;
}());
//====创建一个不可变得类,它的属性,方法都是不可变得===
//===Object.defineProperty()和Object.defineProperties（）可以用来创建新属性，也可以修改已有属性的特性。
// 更改或设置属性描述时,未指定的属性保持已有值,默认是false
function Range(from,to){
    var props = {
        from:{value:from,enumerable:true,writable:false,configurable:false},
        to:{value:to,enumerable:true,writable:false,configurable:false}
    };
    if(this instanceof Range) Object.defineProperties(this,props);
    else return Object.create(Range.prototype,props);
}
//添加不可变方法,除了value,其它都是false
Object.defineProperties(Range.prototype,{
    includes:{value:function(x){return this.from<=x && x<=this.to;}},
    foreach:{value:function(f){for(var x=Math.ceil(this.from);x<=this.to;x++) f(x)}}
});
//=====设置属性描述的工具函数========
function freezeProps(o){
    var props = (arguments.length == 1)     //如果只有一个参数
        ?Object.getOwnPropertyNames(o)      //使用所有属性
        :Array.prototype.slice.call(arguments,1);  //否则传入了指定名字的属性
    props.forEach(function(n){
        //if(!Object.getOwnPropertyDescriptor(o,n).configurable) return; //忽略不可配置属性
        Object.defineProperty(o,n,{writable:false,configurable:false});
    });
    return o;
}
function hideProps(o){
    var props = (arguments.length == 1)
        ?Object.getOwnPropertyNames(o)
        :Array.prototype.slice.call(arguments,1);
    props.forEach(function(n){
        //if(!Object.getOwnPropertyDescriptor(o,n).configurable) return;
        Object.defineProperty(o,n,{enumerable:false});
    });
    return o;
}
//==使用以上工具函数
function Range1(from,to){
    this.from = from;
    this.to = to;
    freezeProps(this);
}
Range1.prototype = hideProps({
    constructor:Range1,
    includes:function(x){return this.from<=x && x<= this.to;},
    foreach:function(f){for(var x=Math.ceil(this.from);x<=this.to;x++) f(x)},
    toString:function(){return '('+this.from+'...'+this.to+')'}
});
var r = new Range1(4,6);
r.from = 1;
r.to = 8;
console.log(r.from); //4 无法修改
console.log(r.to);
//==========封装对象的私有状态(构造函数的属性)======
function Range2(from,to){
    function getFrom(){return from;}
    function getTo(){return to;}
    function setFrom(f){ from = f;}
    function setTo(t){ to = t;}
    Object.defineProperties(this,{
        from:{get:getFrom,set:setFrom,enumerable:true,configurable:false},
        to:{get:getTo,set:setTo,enumerable:true,configurable:false}
    });
}
Range2.prototype = hideProps({
    constructor:Range1,
    includes:function(x){return this.from<=x && x<= this.to;},
    foreach:function(f){for(var x=Math.ceil(this.from);x<=this.to;x++) f(x)},
    toString:function(){return '('+this.from+'...'+this.to+')'}
});