why prototype need a instance not the function self
<p>When we use prototype . we use like</p>

<pre><code>function classA(){

}
function classB(){

}

classB.prototype = new classA();
</code></pre>

<p>why should we write it like that? why isn't it?</p>

<pre><code>classB.prototype = classA;
</code></pre>

<p>after I set the prototype is classA; then I log the classB.prototype. the console log like following</p>

<p>function classA(){
}</p>

<p>what's that mean? I try to add some method into classA but I can NOT call them by using classB.prototype.BLABLA.</p>

<p>my english is not so good. so . I don't know if I explain it well or not.</p>
