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    <blockquote> <p>This lead me to think that I haven't set the Object's prototype, merely created a property called prototype, and set that to a new Sprite.</p> </blockquote> <p>That's right. Also, you are not making use of the function's prototype at all, since you assign each function directly to the instance (<code>this.Draw = function() ...</code>) instead of the prototype.</p> <hr> <p>In JavaScript you have something called <em>constructor functions</em>. Every function called with the <code>new</code> operator is a constructor function.</p> <p>When a function is called that way (<code>new SomeFunc()</code>), a new object is created (lets call it an <em>isntance</em>) which inherits from the object referenced by <code>SomeFunc.prototype</code> and this instance is available inside that function via <code>this</code>.</p> <p>Now, inheritance basically comes down to having a prototype (<code>SomeFunc.prototype</code>) which instead of being an (nearly) empty object (the default), inherits from another function's prototype.</p> <p><strong>Example:</strong></p> <pre><code>function A(name) { // `this` refers to a new instance // lets set some properties: this.name = name; } // all "class" methods should be assigned to the prototype A.prototype.getName = function() { return this.name; }; // lets create a child "class" function B(name, place) { // we have to call the parents constructor with the current instance // and the arguments we want to pass on. // this is like `super(name)` in Java or `A.__init__(self, name)` in Python // (or `super(B, self).__init__(name)` in Python) A.call(this, name); this.place = place; } // here we connect A's prototype with B's prototype in a way that they // stay independent inherits(B, A); // B's "class" methods B.prototype.getPlace = function() { return this.place; }; // now we can do var b = new B('SomeName', 'SomePlace'); alert(b.getName()); alert(b.getPlace()); </code></pre> <p>This is how <code>inherits</code> could look like (this implementation is used by the Google Closure library):</p> <pre><code>function inherits(Child, Parent) { var Tmp = function() {}; Tmp.prototype = Parent.prototype; Child.prototype = new Tmp(); Child.prototype.constructor = Child; } </code></pre> <p>You see that <code>Child.prototype</code> refers to an instance of <code>Tmp</code>. But <code>Tmp</code>'s prototype is the same as <code>Parent</code>'s prototype. That means, the instance returned by <code>new Tmp()</code> inherits from <code>Parent</code>'s prototype, and since this instance is the prototype of <code>Child</code>, all instances of <code>Child</code> will inherit from <code>Parent.prototype</code> as well.</p> <p>With ECMAScript 5, this can be simplified to </p> <pre><code>Child.prototype = Object.create(Parent.prototype); Child.prototype.constructor = Child; </code></pre> <p>but it's essentially the same. It creates a new object which inherits from <code>Parent.prototype</code>.</p> <hr> <p><strong>Further reading:</strong></p> <ul> <li><a href="https://stackoverflow.com/questions/7944880/js-confusion-about-inheritance">JS: Confusion about inheritance</a></li> <li><a href="https://developer.mozilla.org/en/JavaScript/Guide/Inheritance_constructor_prototype" rel="nofollow noreferrer">MDN - Inheritance and the prototype chain</a></li> <li><a href="https://developer.mozilla.org/en/JavaScript/Guide/Inheritance_Revisited" rel="nofollow noreferrer">MDN - Inheritance revisited</a></li> <li><a href="https://developer.mozilla.org/en/JavaScript/Reference/Operators/new" rel="nofollow noreferrer">MDN - <code>new</code></a></li> <li><a href="https://developer.mozilla.org/en/JavaScript/Reference/Operators/this" rel="nofollow noreferrer">MDN - <code>this</code></a></li> <li><a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call" rel="nofollow noreferrer">MDN - <code>.call()</code></a></li> </ul>
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    1. USFelix Kling
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    1. COThanks, I implemented your changes, and I understand prototyping a bit more now
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      1. USLuke O'Brien
 

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