javascript Ö® prototype

function MyObject1(formalParameter){
    alert("MyObject1");    
    this.testNumber = formalParameter;
    //1
    this.toString= function(){
       alert("MyObject1:"+this.testNumber);
    };    
}
function MyObject2(formalParameter){
    alert("MyObject2");   
    this.testString = formalParameter;
    //2
    this.toString= function(){
       alert("MyObject2:"+this.testString);
    };    
}
MyObject2.prototype = new MyObject1( 8 );
var objectRef = new MyObject2( "String_Value" );
alert(objectRef);
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MyObject1
MyObject2
String_Value
undefined(Ϊʲô»á³öÏÖ£¿)
×¢ÊÍ2ÒÔϽá¹ûΪ8
×¢ÊÍ1ºÍ2ÒÔϽá¹ûΪ[object Object]
alert(MyObject2);  µ÷ÓÃÁËFunction.prototype.toString
var ....=(function() {return .....})();   Èç¹ûûÓÐreturn£¬()()¾ÍûÓбØÒª
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²Î¿¼ÎÄÕ http://www.cn-cuckoo.com/wordpress/wp-content/uploads/2007/08/JavaScriptClosures.html