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POHow to alter a prototype's method without overriding it?
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  1. POHow to alter a prototype's method without overriding it?
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    copied!<p>I need to do the following:</p> <pre><code>function Shape (width, height) { var self = this; self.width = width; self.height = height; self.calculateSurface = function () { return (self.width * self.height); }; }; function Circle (radius) { //make sure width == height == radius. }; Circle.prototype = new Shape; Circle.prototype.constructor = Circle(); function Triangle (base, height) { var self = this; Shape.apply(self, arguments); }; Triangle.prototype = new Shape; Triangle.prototype.constructor = Triangle(); var circle = new Circle(5); var triangle = new Triangle(5, 8); alert(circle.calculateSurface()); alert(triangle.calculateSurface()); </code></pre> <p>Both calls to the base prototype method must return the area of the caller, but without overriding the method.</p> <p>How can I make it return (width * height) / 2 for triangle and (radius * radius) * pi for circle without overriding it?</p> <p>Thanks for your time and all best!</p> <p><strong>EDIT:</strong></p> <pre><code>var output = document.getElementById('output'); function Shape(width, height) { var self = this; self.width = width; self.height = height; }; Shape.prototype.calculateSurface = function () { return (this.width * this.height); }; function Rectangle(width, height) { Shape.apply(this, arguments); }; Rectangle.prototype = new Shape; Rectangle.prototype.constructor = Rectangle; function Triangle(base, height) { Shape.apply(this, arguments); }; Triangle.prototype = new Shape; Triangle.prototype.constructor = Triangle; Triangle.prototype.calculateSurface = function () { return ((this.width * this.height) / 2); }; function Circle(radius) { Shape.apply(this, arguments); }; Circle.prototype = new Shape; Circle.prototype.constructor = Circle; Circle.prototype.calculateSurface = function () { return((this.width * this.width) * Math.PI); }; // testing var outputStr = ""; var outputArr = []; for (var i = 0; i &lt; 30; i++) { var rectangle = new Rectangle(i + 1, i + 2); var triangle = new Triangle(i + 1, i + 2); var circle = new Circle(i + 1); outputArr[i] = rectangle; outputStr += "Rectangle width: &lt;b&gt;" + rectangle.width + "&lt;/b&gt; height: &lt;b&gt;" + rectangle.height + "&lt;/b&gt; area: &lt;b&gt;" + rectangle.calculateSurface() + "&lt;/b&gt;&lt;br /&gt;"; outputArr[i + 1] = triangle; outputStr += "Triangle base: &lt;b&gt;" + triangle.width + "&lt;/b&gt; height: &lt;b&gt;" + triangle.height + "&lt;/b&gt; area: &lt;b&gt;" + triangle.calculateSurface() + "&lt;/b&gt;&lt;br /&gt;"; outputArr[i + 2] = circle; outputStr += "Circle radius: &lt;b&gt;" + rectangle.width + "&lt;/b&gt; area: &lt;b&gt;" + circle.calculateSurface() + "&lt;/b&gt;&lt;br /&gt;&lt;br /&gt;"; }; output.innerHTML = outputStr; </code></pre> <p>It works correctly, I hope I understood it right. <strong>Thanks again!</strong></p>
 

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