My first jquery plugin: prevent any input except allowed by regexp

phoneInput.js.coffee

do ($ = jQuery) ->
  $.fn.extend
    phoneInput: (options) ->
      settings = regexp: /^(\+7|8)\d{0,10}$/
      settings = $.extend settings, options

      getChar = (event) ->
        if event.which == null                 # IE
          return null if event.keyCode < 32   # Special chars
          return String.fromCharCode event.keyCode

        if event.which != 0 && event.charCode != 0   # Any browser except IE
          return null if event.which < 32           # Special chars
          return String.fromCharCode event.which

        # Special chars here
        return null

      return @each () ->
        @.value = '' unless settings.regexp.test @.value

        @.onkeypress = (e) ->
          e = e || window.event

          return if e.ctrlKey || e.altKey || e.metaKey

          char = getChar(event || window.event)
          return unless char

          value = @.value + char
          @.value = value if value == '+' || settings.regexp.test(value)

          false