Here's an example of the Module Pattern, read the comments to understand how it works:
This works, but the property 'firstName', is being used by the getName function, and is public. This means we can just override the property.
How would we create a private property in this case? Well, what if we try the same concept of scoping things to the execution of the constructor function, first attempt:
The function now doesn't have access to the variables, so what if we move this into the scope of the constructor... second attempt:
At first glance, this seems to work, but we actually override the prototype each time the constructor runs... bad! Instead we should rather be defining the function on the actual instance being created:
This then solves the problem of keeping the variables private to each instance. One downside to this then is that each instance is referring to its own function, and not sharing one common function on the prototype, taking up more memory, but giving the advantage of private scope.