Can't instantiate object in javascript (node.js)

Question

Can't instantiate object in javascript (node.js)

Hi can someone tell me why I can't instantiate the following class/object?

function Arbitrage(odds1, odds2, investment)
{
    this.investment = investment;
    this.odds1 = odds1;
    this.odds2 = odds2;

    this.arbPercent = function() {
        return 1.0/this.odds1 + 1.0/this.odds2;
    };

    this.profit = function() {
        return this.investment / this.arbPercent() - this.investment;
    };

    this.individualBets = function() {
        return    {
                odds1bet : this.investment/this.odds1/this.arbPercent(),
                odds2bet : this.investment/this.odds2/this.arbPercent()    
            };
    };
};

module.exports = Arbitrage;

I'm calling it like this:

var utility = require('../businesslogic/utility');
...
router.post('/calculate', function(req, res)
    {
        var arbit = new utility.Arbitrage(req.body.odds1, req.body.odds2, req.body.investment);
        res.json({
            arbPercentage : arbit.arbPercent(),
            profit : arbit.Profit(),
            indvBets : arbit.individualBets()
        });
    });

The first line, var arbit = new utility.Arbitrage(...) is throwing the error. It says TypeError: undefined is not a function

I've checked that utility isn't null or anything like that. Also all the constructor arguments are ok.

I'm not very familiar with javascript, any help would be appreciated. Thanks.

javascript
node.js

Answer 1

You're exporting your Arbitrage class directly, so after you're requiring it

var utility = require('../businesslogic/utility');

utility is actually your Arbitrage class, meaning that typeof utility === 'function'.

I can see two ways of fixing it.

1. Change the way you're requiring your Arbitrage class:

var Arbitrage = require('../businesslogic/utility');
// ...
var arbit = new Arbitrage(...);

2. Or change the way you're exporting it:

exports.Arbitrage = Arbitrage;

Answer 2

it's because of the way you exported it

you should use :

module.exports.Arbitrage = Arbitrage;

And then you can instanciate like this :

var Arbitrage = require('../businesslogic/utility');
var varbitrage = new Arbitrage();