Mandrill API send with multiple attachment file input

mandrill-send.js

// uses FileReader, which is not supported on older browsers

// define the files
var files = $('#fileInputID')[0].files, count = files.length;

// file input validation, only if we actually have files
if (count)
{

  // create an array for the final attachment object values
  var files_arr = [];

  // create an array for promises
  var promises = [];

  // loop through the files to create objects
  for (var i = 0; i < files.length; i++)
  {
    // vars for capture
    var fileResult, obj;

    // vars for name and type of the files
    var ft = files[i].type, fn = files[i].name;

    // reader.onload is async, so create a promise
    var p = new Promise(function(resolve, reject) {
      
      // function to load Reader with callback
      readerFiles(files[i], function(e) {
        // get the file content
        base = e.target.result;
        // convert to base64, required by mandrill
        fileResult = base.substr(base.indexOf(',') + 1);
        // create a new attachment object with the vars needed
        obj = {
          type: ft,
          name: fn,
          content: fileResult
        }
        // push that object to the array
        files_arr.push(obj);
      });
      
      resolve();
      
      // error capture with conditionals can be used
      // if(/* good condition */) {
      //  resolve('success');
      // }
      // else {
      //  reject('failure');
      // }
    });
  }

  // after promises have completed, send
  p.then(function() {
    sendForm(files_arr);
  }).catch(function() {
    // error
  });

  // create the reader file
  function readerFiles(files, onLoadCallback)
  {
    var reader = new FileReader();
    reader.readAsDataURL(files);
    reader.onload = onLoadCallback;
  }
}
else
{
  sendForm();
}

function sendForm(files_arr)
{
  $.ajax({
    type: 'POST',
    url: 'https://mandrillapp.com/api/1.0/messages/send.json',
    data: {
      // this is for illustration only, don't expose your key in production
      // create a server side function instead
      'key': yourkey,
      'message': {
        // all other objects as specified by mandrill API
        'attachments': files_arr
      }
    }
  })

  .done(function(response) {
    // success
  })

  .fail(function(response) {
    // fail
  });
}