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POJavascript constructors with parameters
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  1. POJavascript constructors with parameters
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    copied!<p>In trying to understand javascript constructors, I have been looking at <a href="https://stackoverflow.com/questions/892595/javascript-prototypal-inheritance">this question</a>.</p> <p>It seemed to me that I understood it reasonably, but, ironically, when I tried to run similar code, it did not work for me at all.</p> <p>This is my code</p> <pre><code>function Car(name) { this.Name = name; this.Year = 1999; } Car.prototype.Drive = function() { document.write("My name is '" + this.Name + "' and my year is '" + this.Year + "'. &lt;br /&gt;"); }; SuperCar = function () { }; SuperCar.prototype = new Car(); function SuperCar(name) { Car.call(this, name); } var MyCar = new Car("mycar"); var MySuperCar = new SuperCar("my super car"); MyCar.Drive(); MySuperCar.Drive(); </code></pre> <p>First of all, this line</p> <pre><code>SuperCar = function () { }; </code></pre> <p>was necessary for it to run at all. If I leave it out, I the error "SuperCar is undefined" at this line.</p> <pre><code>SuperCar.prototype = new Car(); </code></pre> <p>I don't really understand why declaring SuperCar as an empty function was necessary.</p> <p>Secondly, when I do run the code I get this result</p> <pre><code>My name is 'mycar' and my year is '1999'. My name is 'undefined' and my year is '1999'. </code></pre> <p>Apparently, for MySuperCar, the SuperCar(name) function is never called, but the Car() is.</p> <p>Adding this line does not help</p> <pre><code>SuperCar.prototype.constructor = SuperCar; </code></pre> <p>Neither does this</p> <pre><code>SuperCar.prototype.constructor = function(name) { Car.call(this, name); }; </code></pre> <p>(I have been running the code inside a script-tag on IE 9 and Chrome 22)</p> <p>How should I properly define a SuperCar constructor taking a name parameter? Or, put it another way, how can I make the new SuperCar("my super car") call behave the way I expected (setting the name to "my super car")?</p>
 

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