## ChangeDispenserController Class

  Provides a simple API for the veding machine change dispenser.

  ### Methods

  #### calculateChange(unitsTendered, price)
  

  **unitsTendered:** An array of instances of some kind of MonetaryUnit subclass.  The units tendered all have the same currency and the amount tendered is greater than price.

  **price:** Number. The units tendered match the currency for price, which is why price is just a number.

  **Returns** true if change will successfully 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.  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, `someChangeDispenserInstance.UnitedStatesPennyUnit` would give you an array containing all available 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. "UnitedStatesDimeUnit"),

  		unitInfo: {

  			monetaryValue: 0.1,
  			currency: "USD",
  			currencySymbol: "$"

  		}

  	},
  	// ...

  ]

  ```

  
  #### 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 is not in the monetary unit properties, i.e. `someChangeDispenserInstance.UnitedStatesPennyUnit`.