function Person(name, age, job){ //properties this.name = name; this.age = age; this.job = job; //methods if (typeof this.sayName != "function"){ Person.prototype.sayName = function(){ alert(this.name); }; } } var friend = new Person("Nicholas", 29, "Software Engineer"); friend.sayName();
13、寄生构造函数模式
function Person(name, age, job){ var o = new Object();//依赖全局对象初始化一个对象，然后再返回这个对象 o.name = name; o.age = age; o.job = job; o.sayName = function(){ alert(this.name); }; return o; } var friend = new Person("Nicholas", 29, "Software Engineer"); friend.sayName(); //"Nicholas" function SpecialArray(){ //create the array var values = new Array(); //add the values values.push.apply(values, arguments); //assign the method values.toPipedString = function(){ return this.join("|"); }; //return it return values; } var colors = new SpecialArray("red", "blue", "green"); alert(colors.toPipedString()); //"red|blue|green" alert(colors instanceof SpecialArray);
上诉方法有一点说明下，由于它是依赖外层对象来创建一个新对象，因此不能依赖 instanceof方法来确定属性和方法的来源！它实际上和构造函数的没有关系！
14、稳妥构造函数模式
function Person(name, age, job){ var o = new Object(); o.sayName = function(){ alert(name); }; return o; } var friend = Person("Nicholas", 29, "Software Engineer"); friend.sayName(); //"Nicholas"
此方法不依赖任何new this 关键符！如果要访问对象的方法和属性，只能通过对象已经定义好的方法来获取！
15、继承
javascript实现继承是通过原型链来实现的
function SuperType(){ this.property = true;//定义一个属性 } SuperType.prototype.getSuperValue = function(){//定义的原型方法 return this.property; }; function SubType(){ this.subproperty = false; } //inherit from SuperType SubType.prototype = new SuperType(); SubType.prototype.getSubValue = function (){ return this.subproperty; }; var instance = new SubType(); alert(instance.getSuperValue()); //true alert(instance instanceof Object); //true alert(instance instanceof SuperType); //true alert(instance instanceof SubType); //true alert(Object.prototype.isPrototypeOf(instance)); //true alert(SuperType.prototype.isPrototypeOf(instance)); //true alert(SubType.prototype.isPrototypeOf(instance)); //true SubType继承SuperType的方法和属性，因此当instance可以直接调用SuperType的方法！ function SuperType(){ this.property = true; } SuperType.prototype.getSuperValue = function(){ return this.property; }; function SubType(){ this.subproperty = false; } //inherit from SuperType SubType.prototype = new SuperType(); //new method SubType.prototype.getSubValue = function (){ return this.subproperty; }; //override existing method SubType.prototype.getSuperValue = function (){ return false; }; var instance = new SubType(); alert(instance.getSuperValue()); //false
上面的例子说明，重写的原型会覆盖之前继承的原型，最后返回的往往不是预期的效果
function SuperType(){ this.property = true; } SuperType.prototype.getSuperValue = function(){ return this.property; }; function SubType(){ this.subproperty = false; } //inherit from SuperType SubType.prototype = new SuperType(); //使用字面量添加的方法导致上面的方法失效了 SubType.prototype = { getSubValue : function (){ return this.subproperty; }, someOtherMethod : function (){ return false; } }; var instance = new SubType(); console.log(instance); alert(instance.getSuperValue()); //error!
下面的例子也说明重写原型带来的风险
function SuperType(){ this.colors = ["red", "blue", "green"]; } function SubType(){ } //inherit from SuperType SubType.prototype = new SuperType(); var instance1 = new SubType(); instance1.colors.push("black"); alert(instance1.colors); //"red,blue,green,black" var instance2 = new SubType(); alert(instance2.colors); //"red,blue,green,black"
原型共享导致两个不同的对象调用的同一个数据
16、借用构造函数来实现继承
function SuperType(){ this.colors = ["red", "blue", "green"]; } function SubType(){ //inherit from SuperType SuperType.call(this); } var instance1 = new SubType(); instance1.colors.push("black"); alert(instance1.colors); //"red,blue,green,black" var instance2 = new SubType(); alert(instance2.colors); //"red,blue,green"
传递参数
function SuperType(name){ this.name = name; } function SubType(){ //inherit from SuperType passing in an argument SuperType.call(this, "Nicholas"); //instance property this.age = 29; } var instance = new SubType(); alert(instance.name); //"Nicholas"; alert(instance.age); //29
17、组合继承方式