# ChangeDispenserController Class
  
  #### calculateChange(unitsTendered, price)
  
  **unitsTendered:** An array of instances of some kind of MonetaryUnit subclass.  You can assert that the units tendered all have the same currency and that the amount tendered is greater than price.
  **price:** Number. You can assert that the units tendered match the currency for price, which is why price is just a number.
  
  **Returns** true if change can succesfully be dispensed, otherwise returns false to issue a refund and cancel the product.
  
  # ChangeDispenser Class
  An instance of ChangeDispenser is programmed to physically know what change it has to dispense and physically how to dispense it.  Assume that ChangeDispenser is a thin JavaScript layer over native code.
  
  ### Properties
  For every currency unit available, the JavaScript layer dynamically defines properties that match the class name of the monetary units using Object.defineProperty. It defines the properties as read-only properties using getter methods that return new arrays.
  The new arrays returned from these properties are not referenced internally. For example, `var availablePennies = someChangeDispenserInstance.UnitedStatesPennyUnit;` would give you an array containing instances of UnitedStatesPennyUnit.
  
  ### Methods
  #### unitsAvailable(currency)
  Describes the types of monetary units available to dispense.
  
  **currency:** A String value for the currency, i.e. "USD".
  
  **Returns** an array of objects describing the availablity of monetary units that match the curreny passed in, sorted in descending monetaryValue:
  [
  	{
  		propertyName: String (i.e. "UnitedStatesPennyUnit"),
  		unitInfo: {
  			monetaryValue: Number,
  			currency: String,
  			currencySymbol: String
  		}
  	}
  ]
  
  #### dispense(units)
  Physically dispenses change for all of the monetary unit instances that you pass in.
  
  **units:** An array of instances of some kind of MonetaryUnit subclass.
  
  **Throws** an error synchronously if any instance does not exist in its Column Properties.