diff --git a/src/main/webapp/index.jsp b/src/main/webapp/index.jsp
index c0ccd3c..8cf6ee5 100644
--- a/src/main/webapp/index.jsp
+++ b/src/main/webapp/index.jsp
@@ -34,7 +34,7 @@
                 </div>
                 <div class="center">
                     <div class="input-field col s12">
-                        <select id="day" onchange="updateDays()">
+                        <select id="day" onchange="changeDay()">
                             <option value="0">Montag</option>
                             <option value="1">Dienstag</option>
                             <option value="2">Mittwoch</option>
diff --git a/src/main/webapp/js/cache.js b/src/main/webapp/js/cache.js
index 23d1187..6f5f803 100644
--- a/src/main/webapp/js/cache.js
+++ b/src/main/webapp/js/cache.js
@@ -1,9 +1,6 @@
 $(document).ready(function () {
     let dataset = $('#dataset');
-    $.ajax({
-        url: 'files',
-        dataType: 'json'
-    }).done(function (results) {
+    request('files').then(results => {
         dataset.empty();
         for (const result of results) {
             dataset.append($("<option></option>")
@@ -16,15 +13,24 @@ $(document).ready(function () {
     updateShoppingTimesChart();
 });
 
+/**
+ * update all charts with correct values for dataset
+ */
 function updateCache() {
     let selected = $('#dataset :selected');
-
     if (selected.index() !== -1) {
         updateWeekOverviewChart(selected.val());
         updateShoppingTimesChart(selected.val());
     }
+
 }
 
+/**
+ * request json data
+ * @param url base url
+ * @param id dataset id
+ * @returns {Promise<result>}
+ */
 function request(url, id) {
     return new Promise(((resolve, reject) => {
         if (typeof id !== 'undefined') {
@@ -36,10 +42,14 @@ function request(url, id) {
                 resolve(data);
             });
         }
-
     }));
 }
 
+/**
+ * only for use inside this file, javascript has no better way
+ * @param url url
+ * @returns {Promise<result>}
+ */
 function requestInternal(url) {
     return new Promise(((resolve, reject) => {
         $.ajax({
diff --git a/src/main/webapp/js/shopping_times.js b/src/main/webapp/js/shopping_times.js
index 02f8047..c5d85dc 100644
--- a/src/main/webapp/js/shopping_times.js
+++ b/src/main/webapp/js/shopping_times.js
@@ -56,16 +56,15 @@ function updateShoppingTimesChart(id) {
     if(typeof id !== 'undefined') {
         request('shopping_times', id).then(function (data) {
            shopping_result = data;
-            updateDays();
+            changeDay();
         });
     }else request('shopping_times').then(function(data) {
         shopping_result = data;
-        updateDays();
+        changeDay();
     });
 }
 
-
-function updateDays() {
+function changeDay() {
     if(typeof shopping_result["Montag"] !== 'undefined') {
         let e = document.getElementById("day");
         let value = e.options[e.selectedIndex].text;
diff --git a/src/main/webapp/js/week_overview.js b/src/main/webapp/js/week_overview.js
index dc5bc92..ee3d77c 100644
--- a/src/main/webapp/js/week_overview.js
+++ b/src/main/webapp/js/week_overview.js
@@ -1,6 +1,6 @@
 let week_result;
 
-let week_overview = new Chart(document.getElementById("overview_chart"), {
+let week_overview = new Chart($("#overview_chart"), {
     type: 'line',
     data: {
         labels: [0, 0, 0, 0, 0],
@@ -55,19 +55,18 @@ let week_overview = new Chart(document.getElementById("overview_chart"), {
 });
 
 function updateWeekOverviewChart(id) {
-
-    if(typeof id !== 'undefined') {
+    if (typeof id !== 'undefined') {
         request('week_overview', id).then(function (data) {
             week_result = data;
             updateWeekOverview();
         });
-    }else request('week_overview').then(function(data) {
+    } else request('week_overview').then(function (data) {
         week_result = data;
         updateWeekOverview();
     });
 }
-function updateWeekOverview() {
 
+function updateWeekOverview() {
     week_overview.data.labels = week_result.labels;
     week_overview.data.datasets[0].data = week_result.count;
     week_overview.data.datasets[1].data = week_result.revenue;