How to implement one click upload?
Here is how you would create an auto save after selecting an upload file(s) in D8.

upload_autosave.libraries.yml

auto:
  version: 1.0
  js:
    js/auto.js: {}
  dependencies:
      - core/jquery


upload_autosave.module

/**
 * Implements hook_form_alter().
 * Adds JS file to all forms
 */
function upload_autosave_form_alter(&amp;$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
    $form['#attached']['library'][] = 'upload_autosave/auto';
}


/js/auto.js

(function ($) {
  Drupal.behaviors.upload_autosave = {
    attach: function (context, settings) {
    if ($('.image-widget-data').length || $('.field--type-file').length){
      $('.js-hide.button.js-form-submit.form-submit').remove();
      $('form', context).on('change', 'input.form-file', function() {  
        $('#edit-actions .button.js-form-submit.form-submit')[0].click();
        $(".details-wrapper").html("&lt;img src='/modules/upload_autosave/images/loading.gif'&gt;");
        $('#edit-actions').fadeOut(1000);
      }); 
     }
    }
  };
})(jQuery);