JavaScript基础知识3
隐藏成员变量
在函数体内定义的变量为局部变量，离开函数就挂掉了
在函数体内使用this.成员变量名，则为window对象级变量，即全局变量
故需要这样隐藏成员变量，向外只暴露get、set函数
function testClass(name){
var _firstname=name;
return {
getname : function() {
return _firstname;
}
}
}
var obj=new testClass("testName");
alert(obj.getname());
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3、组合构造函数/原型方式写类，采用前面种方式继承
这种方式父类，子类的属性都挂在构造函数里，方法都挂在原型上。
/**
* 父类Polygon:多边形
*/
function Polygon(sides) {
this.sides = sides;
}
Polygon.prototype.setSides = function(s) {this.sides=s;}
/**
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Javascript数据类型
由于javascript是弱类型语言，即定义变量时不必声明其类型
。但这并不意味着变量没有类型。因为赋值时会自动匹配数据类型！
目前用到的基本数据类型
number
boolean
string
var i
i="test";//这时i就成了string类型
var i
i=4;//这时i就成了number类型
常用对象类型<object> ......
