diff --git a/.eslintrc.json b/.eslintrc.json
index a23d0cc..0827a92 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -1,6 +1,7 @@
 {
     "globals": {
-         "Toc": true
+         "Toc": true,
+         "once": true
     },
     "extends": "drupal",
     "rules": {
diff --git a/js/adminbar-helper.js b/js/adminbar-helper.js
index a1a2bce..8385c1e 100644
--- a/js/adminbar-helper.js
+++ b/js/adminbar-helper.js
@@ -1,4 +1,4 @@
-(function($, Drupal) {
+(($, Drupal) => {
   // Helper methods for the administration toolbar
   // - Reposition body and floating menu when user has admin toolbar enabled.
   Drupal.behaviors.clarin_theme_adminbar_helper = {
diff --git a/js/custom.js b/js/custom.js
index c059b79..adfa4c8 100644
--- a/js/custom.js
+++ b/js/custom.js
@@ -3,7 +3,7 @@
  * Global utilities.
  *
  */
-(function($, Drupal) {
+(($, Drupal) => {
   Drupal.behaviors.clarin_theme_custom = {
     attach: function attach(context) {
       if (context !== document) {
@@ -14,7 +14,7 @@
       $(
         ".mailchimp-signup-subscribe-form .form-type-email, .path-search .search-form .form-type-search",
         document
-      ).each(function() {
+      ).each(() => {
         const label = $(this)
           .find("label")
           .text();
@@ -24,17 +24,15 @@
       });
 
       // Header scroll down arrow function
-      $(".paragraph--type--header-large .arrow-down", document).click(
-        function() {
-          $("html, body").animate({ scrollTop: "+=660px" }, 800);
-        }
-      );
+      $(".paragraph--type--header-large .arrow-down", document).click(() => {
+        $("html, body").animate({ scrollTop: "+=660px" }, 800);
+      });
 
       // Hide tags if there are more than 2
       $(
         ".node--view-mode-teaser-list .field--name-field-tags, .node--view-mode-teaser-big .field--name-field-tags",
         document
-      ).each(function() {
+      ).each(() => {
         if ($(this).find("li").length > 2) {
           $(this)
             .find("ul")
@@ -46,14 +44,14 @@
       });
 
       // Show tags when clicked on show tags button
-      $(".show-tags", document).click(function() {
+      $(".show-tags", document).click(() => {
         $(this)
           .parent()
           .removeClass("hide-more");
       });
 
       // Auto select input search box
-      $("#searchMenuDropdown", document).on("shown.bs.dropdown", function() {
+      $("#searchMenuDropdown", document).on("shown.bs.dropdown", () => {
         $("#edit-keys-dropdown", $(this))
           .focus()
           .select();
diff --git a/js/slidenav.js b/js/slidenav.js
index 2c68a51..daa6c58 100644
--- a/js/slidenav.js
+++ b/js/slidenav.js
@@ -1,4 +1,4 @@
-(function($, Drupal) {
+(($, Drupal) => {
   // CLARIN slidenav helper methods for the top navbar menu. The slidenav is only used on screens narrower
   // than 1200px and when activated in the theme options.
   // - When the window width is narrower than 1200px, add a click handler to dismiss (slide out) the mobile floating
diff --git a/js/toc.js b/js/toc.js
index e84bfc1..39d68d8 100644
--- a/js/toc.js
+++ b/js/toc.js
@@ -3,13 +3,13 @@
  * Initialize TOC
  *
  */
-(function($, Drupal, once) {
+(($, Drupal, once) => {
   Drupal.behaviors.clarin_theme_toc = {
     attach: function attach(context) {
       if (context === document) {
         $(function initToc() {
-          var navSelector = "#toc";
-          var scopeSelector = "#tocscope";
+          const navSelector = "#toc";
+          const scopeSelector = "#tocscope";
           Toc.init({
             $nav: $(once("selectorID", navSelector, context)),
             $scope: $(once("selectorID", scopeSelector, context))