function fileChangeHandler(event) {
    event.preventDefault()
    var originalEvent = event.originalEvent
    var target = originalEvent.dataTransfer || originalEvent.target
    var file = target && target.files && target.files[0]
    if (!file) {
      return
    }
    displayImage(file)
  }
Handles drop and file selection change events

@param {event} event Drop or file selection change event