I've made a class in my NodeJS app and used `module.exports` along with a `require()` statement to bring it into my main server script:

```
// ./classes/clientCollection.js
module.exports = function ClientCollection() {
    this.clients = [];
}

// ./server.js
var ClientCollection = require('./classes/clientCollection.js');
var clientCollection = new ClientCollection();

```

Now I'd like to add functions onto my class like so:

```
ClientCollection.prototype.addClient = function() {
    console.log("test");
}

```

However when I do this I get the following error:

```
ReferenceError: ClientCollection is not defined

```

How do I properly add functions to a class using prototyping in a NodeJS app?