Handle all keyevents and react if digit or return key.

dig_key.coffee

class DigKey
  constructor: (@catch_elm, @disp_elm, @form_elm) ->
    $(@catch_elm).keydown (event) =>
      kc = event.keyCode
      $(@disp_elm).append dig(kc) if is_num(kc)
      if is_cr(kc)
        $(@form_elm).submit
      else
        $(@disp_elm).append '<br/>' if is_cr(kc)

  is_num = (key_code) ->
    return true if key_code >= 48 && key_code <= 58

  is_cr = (key_code) ->
    key_code == 13

  dig = (key_code) -> (key_code - 48) + ''

window.DigKey = DigKey