Java程序员从笨鸟到菜鸟之（二十九）javascript对象的创建和继承实现

javascript对象的创建

 

JavaScript中定义对象的几种方式（JavaScript中没有类的概念，只有对象）： 

1） 基于已有对象扩充其属性和方法： 

var object = new Object();object.name = "zhangsan";object.sayName = function(name){this.name = name;alert(this.name);}object.sayName("lisi");

 

2）工厂方式 

//工厂方式创建对象/*function createObject(){var object = new Object();object.username = "zhangsan";object.password = "123";object.get = function(){alert(this.username + ", " + this.password);}return object;}var object1 = createObject();var object2 = createObject();object1.get();

带参数的构造方法： 

function createObject(username, password){var object = new Object();object.username = username;object.password = password;object.get = function(){alert(this.username + ", " + this.password);}return object;}var object1 = createObject("zhangsan", "123");object1.get();

 

让一个函数对象被多个对象所共享，而不是每一个对象拥有一个函数对象。 

function get(){alert(this.username + ", " + this.password);}function createObject(username, password){var object = new Object();object.username = username;object.password = password;object.get = get;return object;}var object = createObject("zhangsan", "123");var object2 = createObject("lisi", "456");object.get();object2.get();

 

3）构造函数方式 

function Person(){    //在执行第一行代码前，js引擎会为我们生成一个对象 this.username = "zhangsan"; this.password = "123"; this.getInfo = function() {  alert(this.username + ", " + this.password); } //此处有一个隐藏的return语句，用于将之前生成的对象返回}var person = new Person();person.getInfo();

 

         可以在构造对象时传递参数 

function Person(username, password){this.username = username;this.password = password;this.getInfo = function(){alert(this.username + ", " + this.password);}}var person = new Person("zhangsan", "123");person.getInfo();

 

4）原型（“prototype”）方式 

//使用原型（prototype）方式创建对象/*function Person(){}Person.prototype.username = "zhangsan";Person.prototype.password = "123";Person.prototype.getInfo = function(){alert(this.username + ", " + this.password);}var person = new Person();var person2 = new Person();person.username = "lisi";person.getInfo();person2.getInfo();*/

function Person(){}Person.prototype.username = new Array();Person.prototype.password = "123";Person.prototype.getInfo = function(){alert(this.username + ", " + this.password);}var person = new Person();var person2 = new Person();person.username.push("zhangsan");person.username.push("lisi");person.password = "456";person.getInfo();person2.getInfo();

如果使用原型方式对象，那么生成的所有对象会共享原型中的属性，这样一个对象改变了该属性也会反应到其他对象当中。

单纯使用原型方式定义对象无法在构造函数中为属性赋初值，只能在对象生成后再去改变属性值。 

 使用原型+构造函数方式来定义对象，对象之间的属性互不干扰，各  个对象间共享同一个方法 

//使用原型+构造函数方式来定义对象function Person(){this.username = new Array();this.password = "123";}Person.prototype.getInfo = function(){alert(this.username + ", " + this.password);}var p = new Person();var p2 = new Person();p.username.push("zhangsan");p2.username.push("lisi");p.getInfo();p2.getInfo();

 

5）动态原型方式：在构造函数中通过标志量让所有对象共享一个方法，而每个对象拥有自己的属性。 

function Person(){this.username = "zhangsan";this.password = "123";if(typeof Person.flag == "undefined"){alert("invoked");Person.prototype.getInfo = function(){alert(this.username + ", " + this.password);}Person.flag = true;}}var p = new Person();var p2 = new Person();p.getInfo();p2.getInfo();

 

JavaScript中的继承。 

1） 对象冒充 

//继承第一种方式：对象冒充function Parent(username){this.username = username;this.sayHello = function(){alert(this.username);}}function Child(username, password){//下面三行代码是最关键的代码this.method = Parent;this.method(username);delete this.method;this.password = password;this.sayWorld = function(){alert(this.password);}}var parent = new Parent("zhangsan");var child = new Child("lisi", "1234");parent.sayHello();child.sayHello();child.sayWorld();

2） call方法方式。 

call方法是Function对象中的方法，因此我们定义的每个函数都拥有该方法。可以通过函数名来调用call方法，call方法的第一个参数会被传递给函数中的this，从第2个参数开始，逐一赋值给函数中的参数。 

//使用call方式实现对象的继承
function Parent(username){ this.username = username;
 this.sayHello = function() {  alert(this.username); }}
function Child(username, password){ Parent.call(this, username);
 this.password = password;
 this.sayWorld = function() {  alert(this.password); }}
var parent = new Parent("zhangsan");
var child = new Child("lisi", "123");
parent.sayHello();
child.sayHello();child.sayWorld();
 
 

3） apply方法方式 

//使用apply方法实现对象继承function Parent(username){this.username = username;this.sayHello = function(){alert(this.username);}}function Child(username, password){Parent.apply(this, new Array(username));this.password = password;this.sayWorld = function(){alert(this.password);}}var parent = new Parent("zhangsan");var child = new Child("lisi", "123");parent.sayHello();child.sayHello();child.sayWorld();

 

4）原型链方式（无法给构造函数传参数） 

//使用原型链（prototype chain）方式实现对象继承function Parent(){}Parent.prototype.hello = "hello";Parent.prototype.sayHello = function(){alert(this.hello);}function Child(){}Child.prototype = new Parent();Child.prototype.world = "world";Child.prototype.sayWorld = function(){alert(this.world);}var child = new Child();child.sayHello();child.sayWorld();

5）混合方式（推荐） 

//使用混合方式实现对象继承(推荐)function Parent(hello){this.hello = hello;}Parent.prototype.sayHello = function(){alert(this.hello);}function Child(hello, world){Parent.call(this, hello);this.world = world;}Child.prototype = new Parent();Child.prototype.sayWorld = function(){alert(this.world);}var child = new Child("hello", "world");child.sayHello();child.sayWorld();