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copied!<p>I'd suggest the following pattern which makes use of a <a href="https://bitbucket.org/cggaertner/js-hacks/src/master/clone.js" rel="nofollow noreferrer"><code>clone</code> function</a> to inherit from the protoypes and not instances:</p> <pre><code>function Shape(x, y) { this.x = x; this.y = y; } Shape.prototype.draw = function() { throw new Error('Arbitrary shapes cannot be drawn'); }; function Square(x,y,side) { Shape.call(this, x, y); // call super constructor this.side = side; } // inherit from `Shape.prototype` and *not* an actual instance: Square.prototype = clone(Shape.prototype); // override `draw()` method Square.prototype.draw = function() { gotoXY(this.x,this.y); lineTo(this.x+this.side, this.y); // ... }; </code></pre> <p>It's important that methods reside in the prototype (which is as it should be anyway for performance reasons) so you can call the methods of a super class via</p> <pre><code>SuperClass.prototype.aMethod.call(this, arg1, arg2); </code></pre> <p>With some <a href="https://bitbucket.org/cggaertner/js-hacks/src/master/class5.js" rel="nofollow noreferrer">syntactic sugar</a>, you can make JS look like a classical class-based language:</p> <pre><code>var Shape = Class.extend({ constructor : function(x, y) { this.x = x; this.y = y; }, draw : function() { throw new Error('Arbitrary shapes cannot be drawn'); } }); var Square = Shape.extend({ constructor : function(x, y, side) { Shape.call(this, x, y); this.side = side }, draw : function() { gotoXY(this.x,this.y); lineTo(this.x+this.side, this.y); // ... } }); </code></pre>

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