js对象笔记
对象基本概念
js支持以下几种对象:
1.用户自定义对象
2.核心或内置对象(Date,String,Number等)
3.浏览器对象(BOM)
4.文档对象(DOM)
对象的方法：
把一个函数名赋给属性，则这个属性将作为对象的一个方法使用。
<script type="text/javascript">
var toy = new Object();
toy.color = "red";
toy.display = printObject();
function printObject() {
alert(toy.color);
}
toy.display();
</script>结果：red
创建“类”及其对象：
js不像Java或C++中有类的机制，而是通过函数来定义。
<script type="text/javascript">
function Book() {
this.name="abc";
}
var bookObj = new Book;
alert(bookObj.name);
</script>
结果：abc
注：可以动态地为js中的对象添加属性：
<script type="text/javascript">
function Book() {
this.name="abc";
}
var bookObj = new Book;
bookObj.date = "1990"
alert(bookObj.date);
</script>结果:1990
内联函数作为对象的方法：
内联函数在构造函数中直接赋值给属性，免去了第一个例子中先定义再赋值的麻烦。
<script type="text/javascript">
function Book() {
this.name="abc";
this.msg = function() {alert(this.name);}
}
var bookObj = new Book;
bookObj.msg();
</script>
结果：abc
通过对象字面量，可以不通过调用构造函数的方式创建对象。
对象字面量使用key/value的方式来表示对象属性，并且可以嵌套。
语法如下：
1.使用冒号分隔键值
2.使用逗号分隔每组键/值
3.最后一组键值省略逗号
4.整个对象封装在一对括号中
普通对象字面量：
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<meta name="generator" content="PSPad editor, www.pspad.com">
<title></title>
<script type="text/javascript">
var soldier = {
name: undefined,
rank: "captain",
fallIn: function() {
alert("fallIn");
},
fallOut: function() {
alert("fallOut");
}
};
</script>
</head>
<body>
<script type="text/javascript">
soldier.name = "Tom";
alert(soldier.name);
soldier.fallIn();
soldier.fallOut();
</script>
</body>
</html>
运行结果:分别弹出Tom,fallIn，fallOut的对话框
嵌套对象字面量：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<meta name="generator" content="PSPad editor, www.pspad.com">
<title></title>
<script type="text/javascript">
var soldier = {
name: undefined,
rank: "captain",
region:{
name: "nanjing",
phone: 025,
address: {
state: "jiangsu"
}
},
fallIn: function() {
alert("fallIn");
},
fallOut: function() {
alert("fallOut");
}
};
</script>
</head>
<body>
<script type="text/javascript">
alert("city:"+soldier.region.name + "---province:" + soldier.region.address.state);
</script>
</body>
</html>
运行结果：
city:nanjing---province:jiangsu
对象原型（prototype）
当给构造函数的prototype属性赋值时，它们会自动扩展到该类的所有实例。
用prototype属性为对象添加属性
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<meta name="generator" content="PSPad editor, www.pspad.com">
<title></title>
<script type="text/javascript">
function Book(title, author) {
this.title = title;
this.author = author;
}
</script>
</head>
<body>
<script type="text/javascript">
var book1 = new Book("book1", "author1");
var book2 = new Book("book2", "author2");
Book.prototype.publisher = "Jack";
document.write(book1.title+" is published by "+book1.publisher+"<br/>");
document.write(book2.title+" is published by "+book2.publisher);
</script>
</body>
</html>
结果：
页面输出
book1 is published by Jack
book2 is published by Jack
注：添加新属性的方法同样适用于添加新方法。
原型查找链：js中获取对象的属性时，会先查看该属性是否直接定义在那个对象中，如果没有找到，则从prototype属性中寻找，如果还是没有，则向上查找父类对象，一直查到最顶层（Object），这样的过程叫做原型查找链。
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<meta name="generator" content="PSPad editor, www.pspad.com">
<title></title>
<script type="text/javascript">
function Book(title, author) {
this.title = title;
this.author = author;
}
</script>
</head>
<body>
<script type="text/javascript">
var book1 = new Book("book1", "author1");
var book2 = new Book("book2", "author2");
Object.prototype.category = "Science";
Book.prototype.publisher = "Jack";
document.write(book1.title+" is published by "+book1.publisher + " and in the " + book1.category +"<br/>");
document.write(book2.title+" is published by "+book2.publisher + " and in the " + book1.category);
</script>
</body>
</html>输出结果：
book1 is published by Jack and in the Science
book2 is published by Jack and in the Science
这个例子中向上查找的过程：Book中查找publisher->无->Book.prototype查找publisher->有->Book中查找category->无->Book.prototype查找category->无->Object->无->Object.prototype->找到
如果到Object.prototype仍未找到的话，则返回undefined
通过原型实现继承：
js中没有extends关键字，所以实现继承用的是原型的方式。
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<meta name="generator" content="PSPad editor, www.pspad.com">
<title></title>
<script type="text/javascript">
function A() {
this.name="abc";
this.getName = function() {
return this.name;
};
}
function B() {}
//此处实现了B对A的继承
B.prototype = new A();
//B的构造函数赋值
B.prototype.constructor = B;
//子类添加方法
B.prototype.speak = function () {
alert("B is speaking");
}
</script>
</head>
<body>
<script type="text/javascript">
var Bobj = new B;
Bobj.speak();
alert(Bobj.getName());
</script>
</body>
</html>结果：先弹出B is speaking再弹出abc