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copied!<p>There's usually two steps to mimic classical inheritance in javascript:</p> <ol> <li><p>Your subclass constructor needs to call the parent constructor</p></li> <li><p>Your subclass prototype needs to chain into the parent prototype</p></li> </ol> <p>the first step usually looks like</p> <pre><code>function Subclass(blah) { ParentClass.apply(this, arguments); } </code></pre> <p>The second step is trickier. On JS environments that implement the <code>__proto__</code> property, you could do</p> <pre><code>Subclass.prototype = { __proto__ : ParentClass.prototype, subclassMethod1: function() { /* ... */ } } </code></pre> <p>Unless you know exactly where your script will run (like in a node.js environment), you can't rely on <code>__proto__</code> being available to your script, so the general approach will require to use <a href="http://javascript.crockford.com/prototypal.html" rel="nofollow">Crockford's object() method</a>:</p> <pre><code>if (typeof Object.create !== 'function') { Object.create = function (o) { function F() {} F.prototype = o; return new F(); }; } Subclass.prototype = Object.create(ParentClass.prototype); Subclass.prototype.subclassMethod1 = function() { /* ... */ } </code></pre> <p>That's the gist of it. ES5 runtimes may have <code>Object.create()</code> already built-in, and that's fine.</p> <p>There are leftover things to complete the illusion of classic inheritance, such as the ability to easily call a parent class' overriden method. With what we have now, you'd need to have something like <code>ParentClass.prototype.overridenMethod.call(this, arg1, arg2)</code> in your Subclass method. Some OO libraries will helpfully define extra cruft on each of your subclass instances so you can use things like <code>this.superclass.overridenMethod(arg1, arg2)</code>.</p> <p>The implementation of that cruft is left as an exercise to the reader ;)</p>

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