diff --git a/django/contrib/admin/static/admin/js/SelectBox.js b/django/contrib/admin/static/admin/js/SelectBox.js
index 1927b4cefa..e166cf02fc 100644
--- a/django/contrib/admin/static/admin/js/SelectBox.js
+++ b/django/contrib/admin/static/admin/js/SelectBox.js
@@ -31,7 +31,7 @@
                 node.displayed = 1;
                 const node_text = node.text.toLowerCase();
                 for (const token of tokens) {
-                    if (node_text.indexOf(token) === -1) {
+                    if (!node_text.includes(token)) {
                         node.displayed = 0;
                         break; // Once the first token isn't found we're done
                     }
diff --git a/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js b/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
index 8c95df7c12..670d13b226 100644
--- a/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
+++ b/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
@@ -9,10 +9,10 @@
         const name = triggeringLink.id.replace(name_regexp, '');
         let href = triggeringLink.href;
         if (add_popup) {
-            if (href.indexOf('?') === -1) {
-                href += '?_popup=1';
-            } else {
+            if (href.includes('?')) {
                 href += '&_popup=1';
+            } else {
+                href += '?_popup=1';
             }
         }
         const win = window.open(href, name, 'height=500,width=800,resizable=yes,scrollbars=yes');
diff --git a/django/contrib/admin/static/admin/js/cancel.js b/django/contrib/admin/static/admin/js/cancel.js
index cfe06c279f..68c2d6662f 100644
--- a/django/contrib/admin/static/admin/js/cancel.js
+++ b/django/contrib/admin/static/admin/js/cancel.js
@@ -14,10 +14,10 @@
     ready(function() {
         function handleClick(event) {
             event.preventDefault();
-            if (window.location.search.indexOf('&_popup=1') === -1) {
-                window.history.back(); // Go back if not a popup.
+            if (window.location.search.includes('&_popup=1')) {
+                window.close(); // Close the popup.
             } else {
-                window.close(); // Otherwise, close the popup.
+                window.history.back(); // Otherwise, go back.
             }
         }
 
diff --git a/django/contrib/gis/static/gis/js/OLMapWidget.js b/django/contrib/gis/static/gis/js/OLMapWidget.js
index 089ffd38d2..8c1d7feede 100644
--- a/django/contrib/gis/static/gis/js/OLMapWidget.js
+++ b/django/contrib/gis/static/gis/js/OLMapWidget.js
@@ -50,7 +50,7 @@ ol.inherits(GeometryTypeControl, ol.control.Control);
             default_lat: 0,
             default_lon: 0,
             default_zoom: 12,
-            is_collection: options.geom_name.indexOf('Multi') > -1 || options.geom_name.indexOf('Collection') > -1
+            is_collection: options.geom_name.includes('Multi') || options.geom_name.includes('Collection')
         };
 
         // Altering using user-provided options
diff --git a/django/views/i18n.py b/django/views/i18n.py
index b9aa4ac1d4..c4be394900 100644
--- a/django/views/i18n.py
+++ b/django/views/i18n.py
@@ -137,7 +137,7 @@ js_catalog_template = r"""
 
     django.pgettext = function(context, msgid) {
       var value = django.gettext(context + '\x04' + msgid);
-      if (value.indexOf('\x04') != -1) {
+      if (value.includes('\x04')) {
         value = msgid;
       }
       return value;
@@ -145,7 +145,7 @@ js_catalog_template = r"""
 
     django.npgettext = function(context, singular, plural, count) {
       var value = django.ngettext(context + '\x04' + singular, context + '\x04' + plural, count);
-      if (value.indexOf('\x04') != -1) {
+      if (value.includes('\x04')) {
         value = django.ngettext(singular, plural, count);
       }
       return value;