Drupal behavior javascript - https://www.drupal.org/docs/7/api/javascript-api/managing-javascript-in-drupal-7

drupal7.js

Drupal.behaviors.mybehavior = {
  attach: function (context, settings) {
    $('#some_element', context).once('mybehavior', function () {
      // Code here will only be applied to $('#some_element')
      // a single time.
    });
  }
};

drupal8.js

(function ($, Drupal, once) {
  Drupal.behaviors.myModuleBehavior = {
    attach: function (context, settings) {
      once('myCustomBehavior', 'input.myCustomBehavior', context).forEach(function (element) {
        // Apply the myCustomBehaviour effect to the elements only once.
      });
    }
  };
})(jQuery, Drupal, once);