【笔记】 《js权威指南》- 第9章 类和模块 - 9.8 类 ECMAS5

1.让属性不可枚举：

(function () {Object.defineProperty(ClassA.prototype, "propA", {get: propAGetter,set: propASetter,enumerable: false,configurable: false});function checkPropA(self) {if (!(_propAName in self)) {if (!Object.isExtensible(self)) {throw new Error("can't define propA for nonextensible obj");}Object.defineProperty(self, _propAName, {writable: true,value: _propA,enumerable: false,configurable: false});}}function propASetter(v) {checkPropA(this);this[_propAName] += v;};function propAGetter() {checkPropA(this);return this[_propAName];};var _propAName = "_propA";var _propA = 1;})();var b = new ClassB(1, 2, 3);for (var prop in b) {console.log(prop);}b.propA = 4;console.log(b.propA);

打印结果：getParamB, setParamB, porpC, constructor, funcA, funcB, 6

注意不是5，因为在B的构造函数中继承了ClassA的代码this.propA = paramA;

2.定义不可变的类：

定义一些工具函数：e.g.

//将制定名字或者所有的属性设置为不可写以及不可配置的function freezeProps(o) {    var props = (arquments.length == 1) ?        Object.getOwnPropertyNames(o) :        Array.prototype.splice.call(arguments,1);    props.forEach(function(n) {        if (!Object.getOwnPropertyDescriptor(o, n).configurable) return;        Object.defineProperty(o, n, {writable: false, configurable: false});    });    return o;}

 

3.封装对象的状态：

将setter，getter函数更为严格地进行封装：

function setAndGetProp(o, p, g, s) {var obj = {enumerable: true, configurable: false};if (g) obj.get = g;if (s) obj.set = s;Object.defineProperty(o, p, obj);}

//定义构造函数function ClassA(paramA, paramB) {//定义实例字段this.propA = paramA;function getParamB() {return paramB;};function setParamB(value) {paramB = value;};setAndGetProp(this, "paramB", getParamB, setParamB);}