function SuperType(){
      this.property=true;
}
SuperType.prototype.getSuperValue=function(){
      return this.property;
};

function SubType(){
      this.subproperty=false;
}
SubType.prototype=new SuperType(); //这里继承了SuperType
SubType.prototype.getSubValue=function(){
      return this.subproperty;
}
var instance=new SubType();
alert(instance.getSuperValue()); //true