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<div id="pagetitle"><h1>YUI Library Examples: The YUI Global Object: Create Class Hierarchies with <code>extend</code></h1></div>
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<div id="bar-note"><p><strong>Note:</strong> This is YUI 3.x. Looking for <a href="http://developer.yahoo.com/yui/">YUI 2.x</a>?</p></div>
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<div class="yui-u first example" id="main">
<h2>The YUI Global Object: Create Class Hierarchies with <code>extend</code></h2>
<div id="example" class="promo">
<p>
<p>JavaScript supports the notion of class hierarchies. As in other
object-oriented languages, you can create generic classes, then create
specialized subclasses that add or override functionality of the
superclass.</p>
<p>Click the "Show Inheritance" button to do some evaluation of the created object.</p>
</p>
<div class="module example-container ">
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<a href="yui-extend_clean.html" target="_blank">View example in new window.</a>
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<!--BEGIN SOURCE CODE FOR EXAMPLE =============================== -->
<pre style="margin-bottom: 1em">
var chicken = new Chicken();
</pre>
<input type="button" name="demo_btn" id="demo_btn" value="Show Inheritance"/>
<div id="demo">
</div>
<script type="text/javascript">
YUI({base:"../../build/", timeout: 10000, filter:"debug", logInclude: {example:true}}).use("node",
// 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.
function(Y) {
var Bird = function (name) {
this.name = name;
};
Bird.prototype.flighted = true; // Default for all Birds
Bird.prototype.isFlighted = function () { return this.flighted };
Bird.prototype.getName = function () { return this.name };
Chicken = function (name) {
// Chain the constructors
Chicken.superclass.constructor.call(this, name);
};
// Chickens are birds
Y.extend(Chicken, Bird);
// Define the Chicken prototype methods/members
Chicken.prototype.flighted = false; // Override default for all Chickens
showInheritance = function () {
var chicken = new Chicken('Little'),
results = Y.get('#demo');
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Object) ?
"<p>chicken IS an instance of Object.</p>" :
"<p>chicken IS NOT an instance of Object.</p>"));
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Bird) ?
"<p>chicken IS an instance of Y.example.Bird.</p>" :
"<p>chicken IS NOT an instance of Y.example.Bird.</p>"));
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Chicken) ?
"<p>chicken IS an instance of Y.example.Chicken.</p>" :
"<p>chicken IS NOT an instance of Y.example.Chicken.</p>"));
// Chicken instances inherit Bird methods and members
results.set('innerHTML', results.get('innerHTML') +
((chicken.isFlighted()) ?
"<p>chicken CAN fly.</p>" :
"<p>chicken CAN NOT fly.</p>"));
results.set('innerHTML', results.get('innerHTML') +
"<p>chicken's name is " + chicken.getName() + ".</p>");
}
Y.on('click', showInheritance, '#demo_btn');
});
</script>
<!--END SOURCE CODE FOR EXAMPLE =============================== -->
</div>
</div>
</div>
<h2 class="first">Using <code>extend</code></h2>
<h3>Instantiate YUI</h3>
<textarea name="code" class="JScript">
<!-- include yui -->
<script type="text/javascript" src="../../build/yui/yui.js"></script>
YUI({base:"../../build/", timeout: 10000, filter:"debug", logInclude: {example:true}}).use("node",
// 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.
function(Y) {
</textarea>
<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>
<textarea name="code" class="JScript" cols="60" rows="1">
Bird = function (name) {
this.name = name;
};
Bird.prototype.flighted = true; // Default for all Birds
Bird.prototype.isFlighted = function () { return this.flighted };
Bird.prototype.getName = function () { return this.name };
Chicken = function (name) {
// Chain the constructors
Chicken.superclass.constructor.call(this, name);
};
// Chickens are birds
Y.extend(Chicken, Bird);
// Define the Chicken prototype methods/members
Chicken.prototype.flighted = false; // Override default for all Chickens
</textarea>
<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>
<textarea name="code" class="JScript" cols="60" rows="1">
showInheritance = function () {
var chicken = new Chicken('Little'),
results = Y.get('#demo');
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Object) ?
"<p>chicken IS an instance of Object.</p>" :
"<p>chicken IS NOT an instance of Object.</p>"));
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Bird) ?
"<p>chicken IS an instance of Bird.</p>" :
"<p>chicken IS NOT an instance of Bird.</p>"));
results.set('innerHTML', results.get('innerHTML') +
((chicken instanceof Chicken) ?
"<p>chicken IS an instance of Chicken.</p>" :
"<p>chicken IS NOT an instance of Chicken.</p>"));
// Chicken instances inherit Bird methods and members
results.set('innerHTML', results.get('innerHTML') +
((chicken.isFlighted()) ?
"<p>chicken CAN fly.</p>" :
"<p>chicken CAN NOT fly.</p>"));
results.set('innerHTML', results.get('innerHTML') +
"<p>chicken's name is " + chicken.getName() + ".</p>");
}
Y.on('click', showInheritance, '#demo_btn');
</textarea>
<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.
</div>
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<h4>
The YUI Global Object Examples:</h4>
</div>
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<ul>
<li><a href='../yui/yui-core.html'>YUI Core</a></li><li><a href='../yui/yui-more.html'>Load All Modules</a></li><li><a href='../yui/yui-multi.html'>Multiple Instances</a></li><li><a href='../yui/yui-compat.html'>YUI 2.x and 3.x</a></li><li><a href='../yui/yui-loader-ext.html'>YUI Loader - Dynamically Adding YUI and External Modules</a></li><li class='selected'><a href='../yui/yui-extend.html'>Create Class Hierarchies with <code>extend</code></a></li><li><a href='../yui/yui-augment.html'>Compose Classes of Objects with <code>augment</code></a></li><li><a href='../yui/yui-mix.html'>Add Behaviors to Objects with <code>mix</code></a></li><li><a href='../yui/yui-merge.html'>Combine Data Sets with <code>merge</code></a></li><li><a href='../yui/yui-isa.html'>Check Data Types with <code>Lang</code></a></li><li><a href='../yui/yui-ua.html'>Browser Detection with <code>UA</code></a></li> </ul>
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<h4>More The YUI Global Object Resources:</h4>
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