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();