code: function ecommerce(event, track, arr) {
    push.apply(null, [
      '_fxm.ecommerce.' + event,
      track.id() || track.sku(),
      track.name(),
      track.category()
    ].concat(arr || []));
  }
docs: Track ecommerce `event` with `track`
  with optional `arr` to append.
  
  @api private
  @param {string} event
  @param {Track} track
  @param {Array} arr