js简单继承的实现, 改进篇

前文表述: js简单继承的实现

前文问题:
alert(child instanceof base); 打印false, 此处并没有实现真正的继承

改进:
function base() {
this.member = "dnnsun_Member";
this.test=function(){
window.alert('in base');
}
}

base.prototype.test= function() {
window.alert("base member "+this.member);
}

function extend(child, b) {
b.call(child);
child.prototype=new b;
}
var childclass=function(){
this.test=function(){
window.alert("in child");
}
};


extend(childclass, base);

child = new childclass;

window.alert(child.member);
window.alert(child.test);
child.test();
window.alert(child instanceof base);