<script language="javascript" type="text/javascript">
<!--
cat.prototype.changeName = function(name) {
this.name = name;
}
firstCat = new cat("pursur")
firstCat.changeName("Bill")
firstCat.talk() //alerts "Bill says meeow!"
//-->
</script>
就象你所看到的.我们仅只用了 关键字 prototype 实现了在对象定义后马上增加了changeName方法.这个方法被所有的实例共享.
用原型(prototype) 重载 javascript 对象
原型 在自定义对象和有选择性的重载对象上都可以工作.比如 Date() 或 String 这可能是无止境的.
子类和超类
在JAVA 和C++里,有关于类层次的外在概念.每一个类能有一个角色.
In Java and C++, there is an explicit concept of the class hierarchy. i.e. Every class can have a super class from which it inherits properties and methods. Any class can be extended, or sub-classed so the resulting subclass can inherit its parent's behavior. As we have seen, javascript supports prototype inheritance instead of class based. It's possible for inheritance to happen other ways, however.
The following is an example of inheritance through functions.
下面一个例子演示了如何继承通过function .
复制代码 代码如下:
<script language="javascript" type="text/javascript">
<!--
// thanks to webreference
function superClass() {
this.supertest = superTest; //attach method superTest
}
function subClass() {
this.inheritFrom = superClass;
this.inheritFrom();
this.subtest = subTest; //attach method subTest
}
function superTest() {
return "superTest";
}
function subTest() {
return "subTest";
}
var newClass = new subClass();
alert(newClass.subtest()); // yields "subTest"
alert(newClass.supertest()); // yields "superTest"
//-->
</script>
基于继承的原型是遥远的.为 javascript 应用程序在许多场合.
(基于原型的继承在许多javascript的应用场合是非常有用的.)
对象作为联合数组
正如你所知, (.)操作符能够用来存储.[] 操作符用来操作数组.
<script language="javascript" type="text/javascript">
<!--
// These are the same
object.property
object["property"]
//-->
</script>
<SCRIPT LANGUAGE="javascript">
<!--
function Circle (xPoint, yPoint, radius) {
this.x = xPoint;
this.y = yPoint;
this.r = radius;
}
var aCircle = new Circle(5, 11, 99);
alert(aCircle.x);
alert(aCircle["x"]);
//-->
</SCRIPT>
How do I loop through properties in an object?
You need to use a for/in loop.
我们可以通过for in循环来遍历对象的属性。
<script language="javascript" type="text/javascript">
<!--
var testObj = {
prop1 : "hello",
prop2 : "hello2",
prop3 : new Array("hello",1,2)
}
for(x in testObj) alert( x + "-" + testObj[ x ] )
//-->
</script>
<SCRIPT LANGUAGE="javascript">
<!--
var Circle = { x : 0, y : 1, radius: 2 } // another example
for(p in Circle)
alert( p + "-" + Circle[ p ] )
//-->
</SCRIPT>
The important thing to notice is that in the object syntax the property is an identifier, whereas in the array syntax, it's a string. The obvious benefits of using an array syntax to access an object is because of the literal data type, you can easily concat strings and play around with them to access an object. For this to work with the standard syntax, an eval() would need to be used.
应该值得注意的是对象的属性只是一个标识字符，尽管在一个数组里是一个字符串，因为是一个literal的数据类型，所以有利于使用数组的方式的操作一个对象。你也可以很容易的存取一个对象在标准的语句中。这个时候eval()函数可能用得到。
<script language="javascript" type="text/javascript">
<!--
testObj = {
prop1 : "hello",
prop2 : "hello2",
prop3 : new Array("helloa",1,2)
}
for(x in testObj) alert( x + "-" + testObj[ x ] )
var prop3 = testObj["prop3"];
alert(prop3);
//alert(prop[1]);
alert(typeof(prop3));
alert(eval(prop3)[1]);
alert(typeof(eval(prop3)[1]));
//-->
</script>
网上的东西错误的太多了，jb51.net修正后的测试下
[Ctrl+A 全选 注:引入外部Js需再刷新一下页面才能执行]
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