Dropzone.options.myDropzone = {
  // Prevents Dropzone from uploading dropped files immediately
  autoProcessQueue: false,
  init: function() {
    var submitButton = document.querySelector("#submit")
        myDropzone = this; // closure
    submitButton.addEventListener("click", function() {
      myDropzone.processQueue(); // Tell Dropzone to process all queued files.
    });
    // You might want to show the submit button only when 
    // files are dropped here:
    this.on("addedfile", function() {
      // Show submit button here and/or inform user to click it.
    });
  }
};