code: function arrayApi(input, opts, cb) {
      var fd = new FormData(), files = [];
      [].slice.call(input.files).forEach(function(file) {
        fd.append(opts.name, file, file.webkitRelativePath || file.name);
        files.push(file.webkitRelativePath || file.name);
      });
      cb(fd, files);
    }
docs: old prefixed API implemented in Chrome 11+ as well as array fallback