Cannot reference objects defined in other files in express - node.js

Question

I am making an application using the express framework of node.js. I have to use OOP features like inheritance in my application.
I created a simple class in routes/model folder.
exports.Rectangle = function(x,y)
{
this.x = x;
this.y = y;
}
Rectangle.prototype.getArea = function()
{
return (this.x * this.y);
}
Rectangle.prototype.toString = function()
{
var tmp = "Rectangle " + this.x + " : " + this.y;
return tmp;
}
My routes/index.js is like this:
exports.index = function(req, res){
var RectangleClass = require('./model/Rectangle.js');
var rect1 = new RectangleClass.Rectangle(4,6);
console.log(rect1.getArea());
console.log("Rect: " + rect1);
res.send("hello");
};
When I run the app I get the error: 500 ReferenceError: Rectangle is not defined
The error is shown at the Rectangle.prototype.getArea = function() line in routes/model/Rectangle.js
However, if I copy paste the Rectangle class structure in my index.js file, then it is all working. But I have many classes and I do not want to define them all in one file. How can I reference objects defined in other files?

Answer 1

This is the problem in your initial setup:
exports.Rectangle = function(x, y) {
...
}
Rectangle.prototype.getArea = ...
exports.Rectangle doesn't magically create a variable called Rectangle in the current module, hence the undefined error when you try to use Rectangle.prototype.
There are a couple of solutions:
// one solution
var Rectangle = exports.Rectangle = function(x, y) { ... }
Rectangle.prototype.getArea = ...
// another solution
var Rectangle = function(x, y) { ... }
Rectangle.prototype.getArea = ...
exports = Rectangle;
// yet another solution
exports.Rectangle = function(x, y) { ... }
exports.Rectangle.prototype.getArea = ...
Or the one you found out yourself, although creating such a factory function isn't really necessary :)

Answer 2

This suddenly occurred to me. I used a getter method to create and return a Rectangle object. The following changes were made in Rectangle.js.
exports.getRectangle = function(x,y)
{
var r = new Rectangle(x,y);
return r;
}
Rectangle = function(x,y)
{
this.x = x;
this.y = y;
}
The other methods were left unchanged.
In my index.js file, instead of
var r = new RectangleClass.Rectangle(6,4);
I used
var r = RectangleClass.getRectangle(6,4);