How to create a "go back" or "cancel" button on the node add form?

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Adding '#limit_validation_errors' will help override validation,

$form['actions']['submit_cancel'] = array (
  '#type' => 'submit',
  '#weight' => 999,
  '#value' => t('Delete all input and return to previous page'),
  '#submit' => array('MYMODULE_userpageredirect_callback'),
  '#limit_validation_errors' => [],
);

this will cause the form to be rebuild

also you need to add a callback method

 

For drupal 10, you can install a module 'Cancel Button', which will be good for any form already developed

The Cancel Button module allows site administrators to enable a cancel button on entity forms.

https://www.drupal.org/project/cancel_button

For Drupal7 we will need to be smart

  1. lets get the current location:

    $referer_path = $_SERVER['HTTP_REFERER']; 

  2. let set the cancel form element api

          $form['actions']['cancel'] = array(
           '#type' => 'button',
           '#value' => t('Cancel'),
           '#attributes' => [
               'onClick' => 'window.location.replace("'.$referer_path.'"); return false;'
          ],
         ); 

    the page will be refreshed