POS-Server/app/views/customers/new.js.erb

$('#dialog h3.modal-title').html("Agregar Cliente");
// Render the edit form
$('.modal-body-content').html('<%= j render "customers/form_remote" %>')
// Show the dynamic dialog
$('#dialog').modal("show");

// Set focus to the first element
$('#dialog').on('shown.bs.modal', function () {
  	$('.first_input').focus();
 })