Ruby Classes vs JavaScript Constructor Functions

23 Oct 2015 . JavaScript . Comments

#ruby #dbc

So if you have been following along with my blog posts. Last week I wrote a blog post about Ruby classes. So I am gonna continue with the example that I used last week. If you look at the code below, you will see a Ruby class of Money.

class Money
def initialize(denomination,serial_number,country)
  @denomination = denomination
  @serial_number = serial_number

The same object would created in JavaScript like so:

function Money(denomination,serial,country){
this.denomination = denomination,
this.serial_number = serial_number, = country

For review one would create a new Money class in Ruby like so:.

jackson =,"1234","US")

In JavaScript this would be achieved by doing the following:

jackson = new Money(100,"1234","US")

Now lets take the valid method for the Money class in Ruby, seen below.

def valid
  if @serial_number.size = 10

This is where one of the major differences between Ruby classes and the JavaScript Constructor Function differ between the languages. One can create a function that is available to all of the Money objects in JavaScript however it can't be done within the Constructor function. This would be achieved by creating a prototype in Javascript. A prototype is a JavaScript function that is available to all objects of that type. It can be done like so:

Money.prototype.valid = function() {
    if(this.serial_number.length == 10)
        return true;

This will give every Money JS object the ability to check whether its valid or not.