<div class="intro">

<p>Create Class Hierarchies with `extend`</p>

</div>

<div class="example">

{{>yui-extend}}

</div>

<h3>Instantiate YUI</h3>

```

YUI().use('node', function(Y) {

// This method is in the 'oop' module. Since we require 'node'

// for this example, and 'node' requires 'oop', the 'oop' module

// will be loaded automatically.

```

<h3>Creating a class hierarchy</h3>

<p>In this example, we create a class <code>Bird</code> then create a subclass <code>Chicken</code>.</p>

```

{{>yui-extend-js1}}

```

<h3><code>instanceof</code> many classes</h3>

<p>Unlike classes composed with augmentation, subclasses created with <code>extend</code> are also

considered instances of their superclass and all classes higher up the

inheritance tree.</p>

<p>We'll create an instance of <code>Chicken</code> and run some <code>instanceof</code> and method tests against it.</p>

```

{{>yui-extend-js2}}

```

<h3>Other architecture strategies</h3>

<p>Take a look at <code>augment</code> and <code>mix</code> for different strategies of managing your code structure.

<h3>Full Source</h3>

```

YUI().use('node', function(Y) {

{{>yui-extend-js1}}

{{>yui-extend-js2}}

});

```