diff --git a/frontend/frontend.js b/frontend/frontend.js
index ea468aa..76863e7 100644
--- a/frontend/frontend.js
+++ b/frontend/frontend.js
@@ -1,13 +1,14 @@
-function zerocalcareDisplay() {
-
-    zerocalcareOutput = document.getElementById('zerocalcareOutput');
+"use strict"
 
+function zerocalcareDisplay(xhr) {
+    let zerocalcareOutput = document.getElementById('zerocalcareOutput');
+    
     if (xhr.readyState == 4 && xhr.status == 200) {
 
-        var json_obj = JSON.parse(xhr.responseText);
-        var atLeastOne = false; 
+        let json_obj = JSON.parse(xhr.responseText);
+        let atLeastOne = false; 
 
-        for (i in json_obj) {
+        for (let i in json_obj) {
             // Do not display private events
             if (typeof json_obj[i]['CLASS'] === 'string' && json_obj[i]['CLASS'] == 'PRIVATE') {
                 continue;
@@ -15,20 +16,20 @@ function zerocalcareDisplay() {
 
             // Future improvements needed for a better backend output date in ISO format
             // Now we have to parse the string :( very very ugly
-            var date = new Date(json_obj[i]['DATETIME']);
+            let date = new Date(json_obj[i]['DATETIME']);
 
-            var m = new moment(date);
+            let m = new moment(date);
             m.locale('it');
 
-            var eventElement = document.createElement('div');
+            let eventElement = document.createElement('div');
 
-            var titleElement = document.createElement('h5');
+            let titleElement = document.createElement('h5');
             titleElement.appendChild(document.createTextNode(decodeURI(json_obj[i]['SUMMARY'])));
             titleElement.style.fontStyle = 'italic';
             titleElement.classList.add('widget-title');
             eventElement.appendChild(titleElement);
 
-            var contentEventElement = document.createElement('div');
+            let contentEventElement = document.createElement('div');
             eventElement.appendChild(contentEventElement);
 
             // Check if event is not confirmed
@@ -38,7 +39,7 @@ function zerocalcareDisplay() {
                     contentEventElement.style.fontStyle = 'italic';
                     contentEventElement.style.color = 'gray';
                     // Add note
-                    var unconfirmedElement = document.createElement('div');
+                    let unconfirmedElement = document.createElement('div');
                     unconfirmedElement.style.fontWeight = 'bold';
                     unconfirmedElement.appendChild(document.createTextNode('⚠️ Non confermato!'));
                     contentEventElement.appendChild(unconfirmedElement);
@@ -49,31 +50,31 @@ function zerocalcareDisplay() {
                     timeText.style.textDecoration = 'line-through';
                     locationText.style.textDecoration = 'line-through';
                     // Add note
-                    var unconfirmedElement = document.createElement('div');
+                    let unconfirmedElement = document.createElement('div');
                     unconfirmedElement.style.fontWeight = 'bold';
                     unconfirmedElement.appendChild(document.createTextNode('⚠️ Cancellato!'));
                     contentEventElement.appendChild(unconfirmedElement);
                 }
             }
 
-            var dateElement = document.createElement('div');
-            var dateText = document.createElement('span');
+            let dateElement = document.createElement('div');
+            let dateText = document.createElement('span');
             dateText.appendChild(document.createTextNode(m.format('dddd D MMMM YYYY')));
             dateElement.appendChild(document.createTextNode('📅  '));
             dateElement.appendChild(dateText);
             contentEventElement.appendChild(dateElement);
 
-            var timeElement = document.createElement('div');
-            var timeText = document.createElement('span');
-            var timeString = (json_obj[i]['ALLDAY'] == true) ? 'Tutto il giorno' : ('ore ' + m.format('HH:mm'));
+            let timeElement = document.createElement('div');
+            let timeText = document.createElement('span');
+            let timeString = (json_obj[i]['ALLDAY'] == true) ? 'Tutto il giorno' : ('ore ' + m.format('HH:mm'));
             timeText.appendChild(document.createTextNode(timeString));
             timeElement.appendChild(document.createTextNode('⏰ '));
             timeElement.appendChild(timeText);
             contentEventElement.appendChild(timeElement);
 
             // add if location is not empty -- default location should be selected by backend
-            var locationElement = document.createElement('div');
-            var locationText = document.createElement('span');
+            let locationElement = document.createElement('div');
+            let locationText = document.createElement('span');
             if (json_obj[i]['LOCATION'] !== undefined && json_obj[i]['LOCATION'] != '') {
                 locationText.appendChild(document.createTextNode(decodeURI(json_obj[i]['LOCATION'])));
             }
@@ -85,17 +86,17 @@ function zerocalcareDisplay() {
             contentEventElement.appendChild(locationElement);
 
             if (json_obj[i]['DESCRIPTION'] !== undefined && json_obj[i]['DESCRIPTION'] != '') {
-                var descriptionElement = document.createElement('div');
-                var descriptionText = document.createElement('span');
+                let descriptionElement = document.createElement('div');
+                let descriptionText = document.createElement('span');
                 descriptionText.appendChild(document.createTextNode(decodeURI(json_obj[i]['DESCRIPTION'])));
                 descriptionElement.appendChild(document.createTextNode('📝  '));
                 descriptionElement.appendChild(descriptionText);
                 descriptionElement.style.display = "none";
 
                 // Display a clickable "..." button.
-                var moreElement = document.createElement('div');
-                var moreShowText = document.createElement('a');
-                var moreHideText = document.createElement('a');
+                let moreElement = document.createElement('div');
+                let moreShowText = document.createElement('a');
+                let moreHideText = document.createElement('a');
                 
                 moreShowText.appendChild(document.createTextNode('⬇️ Più informazioni...'));
                 moreElement.appendChild(moreShowText);
@@ -135,9 +136,8 @@ function zerocalcareTrigger(url) {
     if (typeof url !== "string")
         return
 
-    xhr = new XMLHttpRequest();
-    xhr.onload = zerocalcareDisplay;
+    let xhr = new XMLHttpRequest();
+    xhr.onload = () => { zerocalcareDisplay(xhr) };
     xhr.open('GET', url, true);
     xhr.send(null);
-
-}
+}
\ No newline at end of file