The below code blocks any non-ajax form from submitting.

  .on('submit', function(event) {
    if (/* Some condition */) {

In Drupal 8, how can we block an Ajax form from being submitted?

Ajax forms do not trigger a form submit handler and I have not been able to block the click event on an Ajaxified form's submit buttons.

For reference, I am trying to fix Issue #3010084: Form submission finishes before file upload is complete


I found the solution here.

// Add submit handler to form.beforeSend.
// Update Drupal.Ajax.prototype.beforeSend only once.
if (typeof Drupal.Ajax !== 'undefined' && typeof Drupal.Ajax.prototype.beforeSubmitOriginal === 'undefined') {
  Drupal.Ajax.prototype.beforeSubmitOriginal = Drupal.Ajax.prototype.beforeSubmit;
  Drupal.Ajax.prototype.beforeSubmit = function (form_values, element_settings, options) {
    if (/* Custom condition */) {
      this.ajaxing = false;
      return false;
    return this.beforeSubmitOriginal();
  • Could you expand on your solution ? How do you implement this code ? I know php and JS but I don't know how AJAX is working in Drupal since I do mostly integration and theming. Mar 26 '19 at 9:41
  • I've used this code in my projet and it didn't work. Then, I've copied the code from your patch drupal.org/files/issues/2018-11-19/2952233-5.patch and it works. But I'm still interested in an explanation because I'm not sure to understand what it does. Mar 26 '19 at 15:35

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