diff --git a/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/clients.volt b/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/clients.volt
index c03d7019e..56cf78ac9 100644
--- a/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/clients.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/clients.volt
@@ -79,7 +79,7 @@ POSSIBILITY OF SUCH DAMAGE.
                     $("#grid-clients > tbody").html('');
                     $.each(data, function(key, value) {
                         var fields = ["sessionId", "userName", "macAddress", "ipAddress", "startTime"];
-                        tr_str = '<tr>';
+                        let tr_str = '<tr>';
                         for (var i = 0; i < fields.length; i++) {
                             if (value[fields[i]] != null) {
                                 tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/vouchers.volt b/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/vouchers.volt
index 92a1cd4bc..2ca1c6f7b 100644
--- a/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/vouchers.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/CaptivePortal/vouchers.volt
@@ -111,7 +111,7 @@ POSSIBILITY OF SUCH DAMAGE.
                         $("#grid-vouchers > tbody > tr").remove();
                         $.each(data, function (key, value) {
                             var fields = ["username", "starttime", "endtime", "expirytime", "state"];
-                            tr_str = '<tr>';
+                            let tr_str = '<tr>';
                             for (var i = 0; i < fields.length; i++) {
                                 if (value[fields[i]] != null) {
                                     tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Core/firmware.volt b/src/opnsense/mvc/app/views/OPNsense/Core/firmware.volt
index 22dbd34c3..8c3daed28 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Core/firmware.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Core/firmware.volt
@@ -31,7 +31,7 @@
      * prepare for checking update status
      */
     function updateStatusPrepare(rerun) {
-        if ($rerun = false) {
+        if (rerun === false) {
             $('#update_status').hide();
             $('#updatelist').show();
         }
@@ -126,7 +126,7 @@
         $('#updatetab > a').tab('show');
         $('#updatestatus').html("{{ lang._('Updating, please wait...') }}");
         $("#audit_all").attr("style","display:none");
-        maj_suffix = '';
+        let maj_suffix = '';
         if ($.upgrade_action == 'maj') {
             maj_suffix = '_maj';
         }
@@ -215,7 +215,7 @@
     function action_may_reboot(pkg_act, pkg_name)
     {
         if (pkg_act == 'reinstall' && (pkg_name == 'kernel' || pkg_name == 'base')) {
-            reboot_msg = "{{ lang._('The firewall will reboot directly after this set reinstall.') }}";
+            const reboot_msg = "{{ lang._('The firewall will reboot directly after this set reinstall.') }}";
 
             // reboot required, inform the user.
             BootstrapDialog.show({
@@ -263,6 +263,7 @@
      */
     function upgrade_ui()
     {
+        let reboot_msg = "";
         if ( $.upgrade_needs_reboot == "1" ) {
             reboot_msg = "{{ lang._('The firewall will reboot directly after this firmware update.') }}";
             if ($.upgrade_action == 'maj') {
@@ -425,9 +426,9 @@
                 if (row['provided'] == "1") {
                     plugin_count += 1;
                 }
-                status_text = '';
-                bold_on = '';
-                bold_off = '';
+                let status_text = '';
+                let bold_on = '';
+                let bold_off = '';
                 if (row['installed'] == "1") {
                     status_text = ' ({{ lang._('installed') }})';
                     bold_on = '<b>';
@@ -468,14 +469,14 @@
             $("#changeloglist > thead").html("<tr><th>{{ lang._('Version') }}</th>" +
             "<th>{{ lang._('Date') }}</th><th></th></tr>");
 
-            installed_version = data['product_version'].replace(/[_-].*/, '');
+            const installed_version = data['product_version'].replace(/[_-].*/, '');
 
             $.each(data['changelog'], function(index, row) {
                 changelog_count += 1;
 
-                status_text = '';
-                bold_on = '';
-                bold_off = '';
+                let status_text = '';
+                let bold_on = '';
+                let bold_off = '';
 
                 if (installed_version == row['version']) {
                     status_text = ' ({{ lang._('installed') }})';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/arp.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/arp.volt
index a70b7f037..5dc965035 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/arp.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/arp.volt
@@ -43,7 +43,7 @@ POSSIBILITY OF SUCH DAMAGE.
                             var html = [];
                             $.each(data, function (key, value) {
                                 var fields = ["ip", "mac", "manufacturer", "intf", "intf_description", "hostname"];
-                                tr_str = '<tr>';
+                                let tr_str = '<tr>';
                                 for (var i = 0; i < fields.length; i++) {
                                     if (value[fields[i]] != null) {
                                         tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/fw_log.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/fw_log.volt
index a4460fc1f..ed47bd66d 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/fw_log.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/fw_log.volt
@@ -44,7 +44,8 @@ POSSIBILITY OF SUCH DAMAGE.
             // fetch new log lines and add on top of grid-log
             ajaxGet('/api/diagnostics/firewall/log/', {'digest': last_digest, 'limit': $("#limit").val()}, function(data, status) {
                 if (data != undefined && data.length > 0) {
-                    while ((record=data.pop()) != null) {
+                    let record;
+                    while ((record = data.pop()) != null) {
                         if (record['__digest__'] != last_digest) {
                             var log_tr = $("<tr>");
                             log_tr.data('details', record);
@@ -128,7 +129,7 @@ POSSIBILITY OF SUCH DAMAGE.
                         var sorted_keys = Object.keys(sender_details).sort();
                         var tbl = $('<table class="table table-condensed table-hover"/>');
                         var tbl_tbody = $("<tbody/>");
-                        for (i=0 ; i < sorted_keys.length; i++) {
+                        for (let i=0 ; i < sorted_keys.length; i++) {
                             if (hidden_columns.indexOf(sorted_keys[i]) === -1 ) {
                                 var row = $("<tr/>");
                                 var icon = null;
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/ndp.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/ndp.volt
index a7957da43..f0734da44 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/ndp.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/ndp.volt
@@ -43,7 +43,7 @@ POSSIBILITY OF SUCH DAMAGE.
                             var html = [];
                             $.each(data, function (key, value) {
                                 var fields = ["ip", "mac", "manufacturer", "intf", "intf_description"];
-                                tr_str = '<tr>';
+                                let tr_str = '<tr>';
                                 for (var i = 0; i < fields.length; i++) {
                                     if (value[fields[i]] != null) {
                                         tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/netflow.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/netflow.volt
index d9d0a98e9..96e77420e 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/netflow.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/netflow.volt
@@ -52,9 +52,9 @@ POSSIBILITY OF SUCH DAMAGE.
                 var data_arr = $.makeArray(data)[0];
                 // sort by flow
                 Object.keys(data_arr).sort().forEach(function (index) {
-                    value = data_arr[index];
+                    let value = data_arr[index];
                     var fields = ["if", "DstIPaddresses", "SrcIPaddresses", "Pkts"];
-                    tr_str = '<tr>';
+                    let tr_str = '<tr>';
                     tr_str += '<td>'+index+'</td>';
                     for (var i = 0; i < fields.length; i++) {
                         if (value[fields[i]] != null) {
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/networkinsight.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/networkinsight.volt
index 2678ea727..2d067c06e 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/networkinsight.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/networkinsight.volt
@@ -169,7 +169,7 @@ POSSIBILITY OF SUCH DAMAGE.
                 break;
           }
           // always round from timestamp to nearest hour
-          from_timestamp =  Math.floor((timestamp_now -duration) / 3600 ) * 3600;
+          const from_timestamp =  Math.floor((timestamp_now -duration) / 3600 ) * 3600;
           return {resolution: resolution, from: from_timestamp, to: timestamp_now};
       }
 
@@ -178,7 +178,7 @@ POSSIBILITY OF SUCH DAMAGE.
        */
       function chart_interface_totals() {
         var selected_time = get_time_select();
-        fetch_params = selected_time.from + '/' + selected_time.to + '/' + selected_time.resolution + '/if,direction' ;
+        const fetch_params = selected_time.from + '/' + selected_time.to + '/' + selected_time.resolution + '/if,direction' ;
         ajaxGet('/api/diagnostics/networkinsight/timeserie/FlowInterfaceTotals/bps/' + fetch_params,{},function(data,status){
             $.each(['chart_intf_in', 'chart_intf_out'], function(idx, target) {
                 let direction = '';
@@ -270,9 +270,8 @@ POSSIBILITY OF SUCH DAMAGE.
                     .donutRatio(0.35)
                     .legendPosition("right")
                     .valueFormat(d3.format(',.2s'));
-                    ;
 
-                chart_data = [];
+                let chart_data = [];
                 data.map(function(item){
                     var label = "(other)";
                     var proto = "";
@@ -331,7 +330,7 @@ POSSIBILITY OF SUCH DAMAGE.
         ajaxGet('/api/diagnostics/networkinsight/top/FlowSourceAddrTotals/'+time_url+'/src_addr/octets/25/',
             {'filter_field': 'if', 'filter_value': $('#interface_select').val()}, function(data, status){
             if (status == 'success'){
-              add_src_pie = function(chart_data_in) {
+              let add_src_pie = function(chart_data_in) {
                   nv.addGraph(function() {
                     var chart = nv.models.pieChart()
                         .x(function(d) { return d.label })
@@ -344,7 +343,7 @@ POSSIBILITY OF SUCH DAMAGE.
                         .legendPosition("right")
                         .valueFormat(d3.format(',.2s'));
 
-                    chart_data = [];
+                    let chart_data = [];
                     chart_data_in.map(function(item){
                         var label = "(other)";
                         if (item.src_addr != "") {
@@ -484,12 +483,11 @@ POSSIBILITY OF SUCH DAMAGE.
                 });
                 // dump  rows
                 data.map(function(item){
-                  let proto;
+                  let proto = '';
                   if (item.protocol in protocol_names) {
                       proto = ' (' + protocol_names[item.protocol] + ')';
-                  } else {
-                      proto = ''
                   }
+                  let service_port;
                   if (item.service_port in service_names) {
                       service_port = service_names[item.service_port];
                   } else {
@@ -609,11 +607,11 @@ POSSIBILITY OF SUCH DAMAGE.
           var date_begin = Date.UTC(now.getUTCFullYear(),now.getUTCMonth(), now.getUTCDate(), 0, 0, 0, 0);
           var date_end  = Date.UTC(now.getUTCFullYear(),now.getUTCMonth(), now.getUTCDate(), 23, 59, 59, 0);
           var tmp_date = new Date();
-          for (i=0; i < 62; i++) {
-              from_date_ts = (date_begin - (24*60*60*1000 * i)) / 1000;
-              to_date_ts = parseInt((date_end - (24*60*60*1000 * i)) / 1000);
+          for (let i=0; i < 62; i++) {
+              let from_date_ts = (date_begin - (24*60*60*1000 * i)) / 1000;
+              let to_date_ts = parseInt((date_end - (24*60*60*1000 * i)) / 1000);
               tmp_date = new Date(from_date_ts*1000);
-              tmp = tmp_date.toISOString().substr(0, 10);
+              let tmp = tmp_date.toISOString().substr(0, 10);
               if (i < 62) {
                   $("#date_detail_from").append($("<option/>").val(from_date_ts).text(tmp));
                   $("#date_detail_to").append($("<option/>").val(to_date_ts).text(tmp));
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/routes.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/routes.volt
index c509e31d2..0771db944 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/routes.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/routes.volt
@@ -39,10 +39,9 @@ POSSIBILITY OF SUCH DAMAGE.
         // update routes
         $("#update").click(function() {
             $('#processing-dialog').modal('show');
+            let resolve = '';
             if ($("#resolve").prop("checked")) {
                 resolve = "yes";
-            } else {
-                resolve = "";
             }
             ajaxGet("/api/diagnostics/interface/getRoutes/", {resolve:resolve}, function (data, status) {
                         if (status == "success") {
@@ -50,7 +49,7 @@ POSSIBILITY OF SUCH DAMAGE.
                             var html = [];
                             $.each(data, function (key, value) {
                                 var fields = ["proto", "destination", "gateway", "flags", "use", "mtu", "netif","intf_description", "expire"];
-                                tr_str = '<tr>';
+                                let tr_str = '<tr>';
                                 for (var i = 0; i < fields.length; i++) {
                                     if (value[fields[i]] != null) {
                                         tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemactivity.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemactivity.volt
index c50c77c7e..5234740ad 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemactivity.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemactivity.volt
@@ -45,7 +45,7 @@ POSSIBILITY OF SUCH DAMAGE.
                             $("#grid-top > tbody").html('');
                             $.each(data['details'], function (key, value) {
                                 var fields = ["PID", "USERNAME", "PRI", "NICE", "SIZE", "RES", "STATE", "C", "TIME", "WCPU", "COMMAND"];
-                                tr_str = '<tr>';
+                                let tr_str = '<tr>';
                                 for (var i = 0; i < fields.length; i++) {
                                     if (value[fields[i]] != null) {
                                         tr_str += '<td>' + value[fields[i]] + '</td>';
diff --git a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemhealth.volt b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemhealth.volt
index 8a65d55a9..cb9104869 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemhealth.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Diagnostics/systemhealth.volt
@@ -109,10 +109,9 @@
         chart.dispatch.on('brush.brushend', function (b) {
             window.onresize = null; // clear any pending resize events
             if (fetching_data == false) {
+                let inverse = false;
                 if ($('input:radio[name=inverse]:checked').val() == 1) {
                     inverse = true;
-                } else {
-                    inverse = false;
                 }
 
                 var detail = $('input:radio[name=detail]:checked').val();
@@ -272,10 +271,9 @@
 
         }
 
+        let inverse = false;
         if ($('input:radio[name=inverse]:checked').val() == 1) {
             inverse = true;
-        } else {
-            inverse = false;
         }
         if (detail === undefined) {
             detail = 0;
@@ -295,7 +293,7 @@
         csvData = [];
 
         // array used for min/max/average table when shown
-        min_max_average = {};
+        let min_max_average = {};
 
         // info bar - hide averages info bar while refreshing data
         $('#averages').hide();
@@ -339,8 +337,9 @@
 
                 // Add zoomlevel buttons/options
                 if ($('input:radio[name=detail]:checked').val() == undefined || zoom_buttons==="") {
-                    for (setcount = 0; setcount < data["sets"].length; ++setcount) {
-                        recordedtime = data["sets"][setcount]["recorded_time"];
+                    for (let setcount = 0; setcount < data["sets"].length; ++setcount) {
+                        const recordedtime = data["sets"][setcount]["recorded_time"];
+                        let detail_text = '';
                         // Find out what text matches best
                         if (recordedtime >= 31536000) {
                             detail_text = Math.floor(recordedtime / 31536000).toString() + " {{ lang._('Year(s)') }}";
@@ -367,7 +366,7 @@
                 $('#stepsize').text(stepsize + " " + scale);
 
                 // Check for enabled or disabled stream, to make sure that same set stays selected after update
-                for (index = 0; index < disabled.length; ++index) {
+                for (let index = 0; index < disabled.length; ++index) {
                     window.resize = null;
                     data["d3"]["data"][index]["disabled"] = disabled[index]; // disable stream if it was disabled before updating dataset
                 }
diff --git a/src/opnsense/mvc/app/views/OPNsense/Proxy/index.volt b/src/opnsense/mvc/app/views/OPNsense/Proxy/index.volt
index 93d676945..7a78c5356 100644
--- a/src/opnsense/mvc/app/views/OPNsense/Proxy/index.volt
+++ b/src/opnsense/mvc/app/views/OPNsense/Proxy/index.volt
@@ -117,7 +117,7 @@
             function show_line(the_id) {
                 $('tr[for=' + the_id + ']').show();
             }
-            value = $("#pac\\.match\\.match_type").val();
+            let value = $("#pac\\.match\\.match_type").val();
             if (!value) {
                 // retry later
                 setTimeout(update_pac_match_view, 100);
diff --git a/src/opnsense/www/js/opnsense_bootgrid_plugin.js b/src/opnsense/www/js/opnsense_bootgrid_plugin.js
index b1bf4c23a..5f225575e 100644
--- a/src/opnsense/www/js/opnsense_bootgrid_plugin.js
+++ b/src/opnsense/www/js/opnsense_bootgrid_plugin.js
@@ -151,8 +151,8 @@ $.fn.UIBootgrid = function (params) {
                     grid.find(".command-info").on("click", function(e) {
                         if(gridParams['info'] != undefined) {
                             var uuid=$(this).data("row-id");
-                            ajaxGet(url=gridParams['info'] + uuid,
-                                sendData={}, callback=function(data, status) {
+                            ajaxGet(gridParams['info'] + uuid,
+                                {}, function(data, status) {
                                     if(status == 'success') {
                                         var title = data['title'] || "Information";
                                         var message = data['message'] || "A Message";
@@ -184,8 +184,8 @@ $.fn.UIBootgrid = function (params) {
                                 // define save action
                                 $("#btn_"+editDlg+"_save").unbind('click').click(function(){
                                     if (gridParams['set'] != undefined) {
-                                        saveFormToEndpoint(url=gridParams['set']+uuid,
-                                            formid='frm_' + editDlg, callback_ok=function(){
+                                        saveFormToEndpoint(gridParams['set']+uuid,
+                                            'frm_' + editDlg, function(){
                                                 $("#"+editDlg).modal('hide');
                                                 std_bootgrid_reload(gridId);
                                             }, true);
@@ -219,8 +219,8 @@ $.fn.UIBootgrid = function (params) {
                                 // define save action
                                 $("#btn_"+editDlg+"_save").unbind('click').click(function(){
                                     if (gridParams['add'] != undefined) {
-                                        saveFormToEndpoint(url=gridParams['add'],
-                                            formid='frm_' + editDlg, callback_ok=function(){
+                                        saveFormToEndpoint(gridParams['add'],
+                                            'frm_' + editDlg, function(){
                                                 $("#"+editDlg).modal('hide');
                                                 std_bootgrid_reload(gridId);
                                             }, true);
@@ -243,8 +243,8 @@ $.fn.UIBootgrid = function (params) {
                             var uuid=$(this).data("row-id");
                             // XXX must be replaced, cannot translate
                             stdDialogRemoveItem('Remove selected item?',function() {
-                                ajaxCall(url=gridParams['del'] + uuid,
-                                    sendData={},callback=function(data,status){
+                                ajaxCall(gridParams['del'] + uuid,
+                                    {},function(data,status){
                                         // reload grid after delete
                                         std_bootgrid_reload(gridId);
                                     });
@@ -260,8 +260,8 @@ $.fn.UIBootgrid = function (params) {
                         if (gridParams['toggle'] != undefined) {
                             var uuid=$(this).data("row-id");
                             $(this).addClass("fa-spinner fa-pulse");
-                            ajaxCall(url=gridParams['toggle'] + uuid,
-                                sendData={},callback=function(data,status){
+                            ajaxCall(gridParams['toggle'] + uuid,
+                                {},function(data,status){
                                     // reload grid after delete
                                     std_bootgrid_reload(gridId);
                                 });
@@ -289,8 +289,8 @@ $.fn.UIBootgrid = function (params) {
                         $('#'+editDlg).modal({backdrop: 'static', keyboard: false});
                         //
                         $("#btn_"+editDlg+"_save").unbind('click').click(function(){
-                            saveFormToEndpoint(url=gridParams['add'],
-                                formid='frm_' + editDlg, callback_ok=function(){
+                            saveFormToEndpoint(gridParams['add'],
+                                'frm_' + editDlg, function(){
                                     $("#"+editDlg).modal('hide');
                                     std_bootgrid_reload(gridId);
                                 }, true);
@@ -309,7 +309,7 @@ $.fn.UIBootgrid = function (params) {
                             if (rows != undefined){
                                 var deferreds = [];
                                 $.each(rows, function(key,uuid){
-                                    deferreds.push(ajaxCall(url=gridParams['del'] + uuid, sendData={},null));
+                                    deferreds.push(ajaxCall(gridParams['del'] + uuid, {},null));
                                 });
                                 // refresh after load
                                 $.when.apply(null, deferreds).done(function(){
diff --git a/src/opnsense/www/js/opnsense_ui.js b/src/opnsense/www/js/opnsense_ui.js
index 5de9061a1..34868fd9e 100644
--- a/src/opnsense/www/js/opnsense_ui.js
+++ b/src/opnsense/www/js/opnsense_ui.js
@@ -55,7 +55,7 @@
 function saveFormToEndpoint(url,formid,callback_ok, disable_dialog) {
     disable_dialog = disable_dialog || false;
     var data = getFormData(formid);
-    ajaxCall(url=url,sendData=data,callback=function(data,status){
+    ajaxCall(url,data,function(data,status){
         if ( status == "success") {
             // update field validation
             handleFormValidation(formid,data['validations']);
@@ -113,7 +113,7 @@ function mapDataToFormUI(data_get_map) {
 
     var collected_data = {};
     $.each(data_get_map, function(data_index, data_url) {
-        ajaxGet(url=data_url,sendData={}, callback=function(data, status) {
+        ajaxGet(data_url,{}, function(data, status) {
             if (status == "success") {
                 $("form").each(function( index ) {
                     if ( $(this).attr('id') && $(this).attr('id').split('-')[0] == data_index) {
@@ -158,7 +158,7 @@ function updateServiceStatusUI(status)
  */
 function updateServiceControlUI(serviceName)
 {
-    ajaxCall(url="/api/" + serviceName + "/service/status", sendData={}, callback=function(data,status) {
+    ajaxCall("/api/" + serviceName + "/service/status", {}, function(data,status) {
         var status_html = '<span class="label label-opnsense label-opnsense-sm ';
         var status_icon = '';
         var buttons = '';
@@ -184,9 +184,9 @@ function updateServiceControlUI(serviceName)
         commands.forEach(function(command) {
             $("#" + command + "Service").click(function(){
                 $('#OPNsenseStdWaitDialog').modal('show');
-                ajaxCall(url="/api/" + serviceName + "/service/" + command, sendData={},callback=function(data,status) {
+                ajaxCall("/api/" + serviceName + "/service/" + command, {},function(data,status) {
                     $('#OPNsenseStdWaitDialog').modal('hide');
-                    ajaxCall(url="/api/" + serviceName + "/service/status", sendData={}, callback=function(data,status) {
+                    ajaxCall("/api/" + serviceName + "/service/status", {}, function(data,status) {
                         updateServiceControlUI(serviceName);
                     });
                 });
@@ -250,7 +250,7 @@ function formatTokenizersUI() {
 
             // re-init tokenizer items
             sender.tokenize2().trigger('tokenize:clear');
-            for (i=0 ; i < items.length ; ++i) {
+            for (let i=0 ; i < items.length ; ++i) {
               sender.tokenize2().trigger('tokenize:tokens:add', items[i]);
             }
             sender.tokenize2().trigger('tokenize:select');
diff --git a/src/www/firewall_nat_edit.php b/src/www/firewall_nat_edit.php
index 9e3d7d595..cc9c92ba3 100644
--- a/src/www/firewall_nat_edit.php
+++ b/src/www/firewall_nat_edit.php
@@ -374,6 +374,7 @@ $( document ).ready(function() {
 
     // on change event protocol change
     $("#proto").change(function(){
+        let port_disabled = true;
         if ($("#proto").val() == "tcp" ||  $("#proto").val() == "udp" || $("#proto").val() == "tcp/udp") {
             port_disabled = false;
         } else {
diff --git a/src/www/firewall_rules_edit.php b/src/www/firewall_rules_edit.php
index 842e55cd8..0eaf32f5f 100644
--- a/src/www/firewall_rules_edit.php
+++ b/src/www/firewall_rules_edit.php
@@ -595,6 +595,7 @@ include("head.inc");
           } else {
               $("#icmpbox").addClass("hidden");
           }
+          let port_disabled = true;
           // lock src/dst ports on other then tcp/udp
           if ($("#proto").val() == 'tcp' || $("#proto").val() == 'udp' || $("#proto").val() == 'tcp/udp') {
               port_disabled = false;
diff --git a/src/www/firewall_schedule_edit.php b/src/www/firewall_schedule_edit.php
index 6c5691c18..cb3bf4b15 100644
--- a/src/www/firewall_schedule_edit.php
+++ b/src/www/firewall_schedule_edit.php
@@ -226,18 +226,18 @@ function repeatExistingDays(){
   var tempstr, tempstrdaypos, week, daypos, dayposdone = "";
 
   var dayarray = daysSelected.split(",");
-  for (i=0; i<=dayarray.length; i++){
+  for (let i=0; i<=dayarray.length; i++){
     tempstr = dayarray[i];
     tempstrdaypos = tempstr.search("p");
     week = tempstr.substring(1,tempstrdaypos);
     week = parseInt(week);
-    dashpos = tempstr.search("-");
+    const dashpos = tempstr.search("-");
     daypos = tempstr.substring(tempstrdaypos+1, dashpos);
     daypos = parseInt(daypos);
 
-    daydone = dayposdone.search(daypos);
+    const daydone = dayposdone.search(daypos);
     tempstr = 'w' + week + 'p' + daypos;
-    daycell = document.getElementById(tempstr);
+    const daycell = document.getElementById(tempstr);
     if (daydone == "-1"){
       if (daycell.dataset['state'] == "lightcoral")
         daytogglerepeating(week,daypos,true);
@@ -250,11 +250,11 @@ function repeatExistingDays(){
 
 function daytogglerepeating(week,daypos,bExists){
   var tempstr, daycell, dayoriginal = "";
-  for (j=1; j<=53; j++)
+  for (let j=1; j<=53; j++)
   {
     tempstr = 'w' + j + 'p' + daypos;
     daycell = document.getElementById(tempstr);
-    dayoriginalpos =  daysSelected.indexOf(tempstr);
+    const dayoriginalpos =  daysSelected.indexOf(tempstr);
 
     //if bExists set to true, means cell is already select it
     //unselect it and remove original day from daysSelected string
@@ -271,7 +271,7 @@ function daytogglerepeating(week,daypos,bExists){
 
       if (dayoriginalpos != "-1")
       {
-        dayoriginalend = daysSelected.indexOf(',', dayoriginalpos);
+        const dayoriginalend = daysSelected.indexOf(',', dayoriginalpos);
         tempstr = daysSelected.substring(dayoriginalpos, dayoriginalend+1);
         daysSelected = daysSelected.replace(tempstr, "");
 
@@ -284,11 +284,12 @@ function daytoggle(id) {
   var runrepeat, tempstr = "";
   var bFoundValid = false;
 
-  iddashpos = id.search("-");
+  const iddashpos = id.search("-");
   var tempstrdaypos = id.search("p");
   var week = id.substring(1,tempstrdaypos);
   week = parseInt(week);
 
+  let idmod;
   if (iddashpos == "-1")
   {
     idmod = id;
@@ -309,7 +310,7 @@ function daytoggle(id) {
     if (daycell != null){
       if (daycell.dataset['state'] == "red"){  // red
         daycell.dataset['state'] = "white";
-        str = id + ",";
+        let str = id + ",";
         daysSelected = daysSelected.replace(str, "");
       }
       else if (daycell.dataset['state'] == "lightcoral")
@@ -345,8 +346,8 @@ function update_month(){
   var indexNum = document.iform.monthsel.selectedIndex;
   var selected = document.iform.monthsel.options[indexNum].text;
 
-  for (i=0; i<=11; i++){
-    option = document.iform.monthsel.options[i].text;
+  for (let month = 0; month < 12; month++){
+    let option = document.iform.monthsel.options[month].text;
     document.popupMonthLayer = document.getElementById(option);
 
     if(selected == option) {
@@ -445,7 +446,7 @@ function addTimeRange(){
 
   if (daysSelected != ""){
     //get days selected
-    for (i=0; i<tempdayarray.length; i++)
+    for (let i=0; i<tempdayarray.length; i++)
     {
       tempstr = tempdayarray[i];
       if (tempstr != "")
@@ -459,7 +460,7 @@ function addTimeRange(){
           nonrepeatingfound = true;
           daypos = tempstr.substring(tempstrdaypos+1, dashpos);
           daypos = parseInt(daypos);
-          monthpos = tempstr.search("m");
+          let monthpos = tempstr.search("m");
           tempstrdaypos = tempstr.search("d");
           month = tempstr.substring(monthpos+1, tempstrdaypos);
           month = parseInt(month);
@@ -560,7 +561,7 @@ function addTimeRange(){
     tempsortArray.sort();
     //clear tempID
     rtempID = "";
-    for (t=0; t<tempsortArray.length; t++)
+    for (let t=0; t<tempsortArray.length; t++)
     {
       if (tempsortArray[t] != ""){
         if (!isFirstdone){
@@ -631,8 +632,8 @@ function addTimeRange(){
 function insertElements(tempFriendlyTime, starttimehour, starttimemin, stoptimehour, stoptimemin, tempdescr, tempTime, tempID){
 
     //add it to the schedule list
-    d = document;
-    tbody = document.getElementById("scheduletable").getElementsByTagName("tbody").item(0);
+    let d = document;
+    let tbody = document.getElementById("scheduletable").getElementsByTagName("tbody").item(0);
     var tr = document.createElement("tr");
     var td = document.createElement("td");
     td.innerHTML= `<span>${tempFriendlyTime}</span>`;
@@ -676,12 +677,12 @@ function clearCalendar(){
   var tempstr, daycell = "";
   //clear days selected
   daysSelected = "";
-  //loop through all 52 weeks
-  for (j=1; j<=53; j++)
+  //loop through all 53 weeks
+  for (let week=1; week<=53; week++)
   {
     //loop through all 7 days
-    for (k=1; k<8; k++){
-      tempstr = 'w' + j + 'p' + k;
+    for (let day = 1; day <= 7; day++){
+      tempstr = 'w' + week + 'p' + day;
       daycell = document.getElementById(tempstr);
       if (daycell != null){
         daycell.dataset['state'] = "white";
@@ -710,7 +711,7 @@ function editRow(incTime, el) {
 
     var starttimehour, descr, days, tempstr, starttimemin, hours, stoptimehour, stoptimemin = "";
 
-    tempArray = incTime.split ("||");
+    let tempArray = incTime.split ("||");
 
     days = tempArray[0];
     hours = tempArray[1];
@@ -733,11 +734,11 @@ function editRow(incTime, el) {
     document.getElementById("timerangedescr").value = descr;
 
     //toggle the appropriate days
-    for (i=0; i<tempdayArray.length; i++)
+    for (let i=0; i<tempdayArray.length; i++)
     {
       if (tempdayArray[i]){
         var tempweekstr = tempdayArray[i];
-        dashpos = tempweekstr.search("-");
+        let dashpos = tempweekstr.search("-");
 
         if (dashpos == "-1")
         {
diff --git a/src/www/foot.inc b/src/www/foot.inc
index e1bf31a3e..e3d2a314b 100644
--- a/src/www/foot.inc
+++ b/src/www/foot.inc
@@ -79,7 +79,7 @@
       $( document ).ready(function() {
         $('.srv_status_act').click(function(event){
           event.preventDefault();
-          params = {};
+          let params = {};
           params['action'] = $(this).data('service_action');
           params['service'] = $(this).data('service');
           params['id'] = $(this).data('service_id');
diff --git a/src/www/index.php b/src/www/index.php
index 679787296..9974a5eee 100644
--- a/src/www/index.php
+++ b/src/www/index.php
@@ -167,7 +167,7 @@ include("fbegin.inc");?>
   }
 
   function configureWidget(selectedDiv) {
-      selectIntLink = '#' + selectedDiv + "-settings";
+      let selectIntLink = '#' + selectedDiv + "-settings";
       if ($(selectIntLink).css('display') == "none") {
           $(selectIntLink).show();
       } else {
@@ -209,7 +209,7 @@ include("fbegin.inc");?>
               // only capture visible widgets
               var index_str = "0000000" + index;
               index_str = index_str.substr(index_str.length-8);
-              col_index = $(this).parent().attr("id").split('_')[1];
+              let col_index = $(this).parent().attr("id").split('_')[1];
               widgetInfo.push($(this).attr('id')+'-container:'+index_str+'-'+col_index+':'+$('input[name='+$(this).attr('id')+'-config]').val());
               index++;
           }
diff --git a/src/www/interfaces.php b/src/www/interfaces.php
index 0b5d67e10..a5f729037 100644
--- a/src/www/interfaces.php
+++ b/src/www/interfaces.php
@@ -1460,7 +1460,7 @@ include("head.inc");
                   var responseTextArr = response.split("\n");
                   responseTextArr.sort();
                   $.each(responseTextArr, function(index, value) {
-                    country = value.split(':');
+                    let country = value.split(':');
                     $('#country').append(new Option(country[0], country[1]));
                   });
                 }
@@ -1695,7 +1695,7 @@ include("head.inc");
               responseTextArr.sort();
               jQuery.each(responseTextArr, function(index, value) {
                 if (value != '') {
-                  providerplan = value.split(':');
+                  let providerplan = value.split(':');
                   $('#providerplan').append(new Option(
                     providerplan[0] + ' - ' + providerplan[1],
                     providerplan[1]
diff --git a/src/www/interfaces_ppps_edit.php b/src/www/interfaces_ppps_edit.php
index c16690634..1192881e6 100644
--- a/src/www/interfaces_ppps_edit.php
+++ b/src/www/interfaces_ppps_edit.php
@@ -281,7 +281,7 @@ include("head.inc");
                   var responseTextArr = response.split("\n");
                   responseTextArr.sort();
                   $.each(responseTextArr, function(index, value) {
-                    country = value.split(':');
+                    let country = value.split(':');
                     $('#country').append(new Option(country[0], country[1]));
                   });
                 }
@@ -359,7 +359,7 @@ include("head.inc");
                 responseTextArr.sort();
                 jQuery.each(responseTextArr, function(index, value) {
                   if (value != '') {
-                    providerplan = value.split(':');
+                    let providerplan = value.split(':');
                     $('#providerplan').append(new Option(
                       providerplan[0] + ' - ' + providerplan[1],
                       providerplan[1]
diff --git a/src/www/javascript/opnsense_legacy.js b/src/www/javascript/opnsense_legacy.js
index 845f20b55..e91bbe0d5 100644
--- a/src/www/javascript/opnsense_legacy.js
+++ b/src/www/javascript/opnsense_legacy.js
@@ -84,7 +84,7 @@ function hook_stacked_form_tables(match)
   $(match).each(function(){
       var root_node = $(this);
       if (root_node.is('table')) {
-          row_number = 0;
+          let row_number = 0;
           // traverse all <tr> tags
           root_node.find('tr').each(function(){
               // only evaluate children under this table or in <thead|tbody|..> element
diff --git a/src/www/javascript/wizard/autosuggest.js b/src/www/javascript/wizard/autosuggest.js
index 886aaddb6..8f04bbddb 100644
--- a/src/www/javascript/wizard/autosuggest.js
+++ b/src/www/javascript/wizard/autosuggest.js
@@ -78,7 +78,7 @@ AutoSuggestControl.prototype.createDropDown = function () {
     this.layer.onmouseup =
     this.layer.onmouseover = function (oEvent) {
         oEvent = oEvent || window.event;
-        oTarget = oEvent.target || oEvent.srcElement;
+        let oTarget = oEvent.target || oEvent.srcElement;
 
         if (oEvent.type == "mousedown") {
             oThis.textbox.value = oTarget.firstChild.nodeValue;
diff --git a/src/www/status_habackup.php b/src/www/status_habackup.php
index f21092664..35dd90463 100644
--- a/src/www/status_habackup.php
+++ b/src/www/status_habackup.php
@@ -143,7 +143,7 @@ include("head.inc");
                 // reload all services
                 $(".xmlrpc_srv_status_act").each(function(){
                     if ($(this).data('service_action') == 'restart') {
-                        params = {};
+                        let params = {};
                         params['action'] = $(this).data('service_action');
                         params['service'] = $(this).data('service_name');
                         params['id'] = $(this).data('service_id');
@@ -152,7 +152,7 @@ include("head.inc");
                 });
             } else if ($(this).data('service_action') != undefined) {
                 // reload single service
-                params = {};
+                let params = {};
                 params['action'] = $(this).data('service_action');
                 params['service'] = $(this).data('service_name');
                 params['id'] = $(this).data('service_id');
diff --git a/src/www/system_authservers.php b/src/www/system_authservers.php
index 707955fdc..6cac986d5 100644
--- a/src/www/system_authservers.php
+++ b/src/www/system_authservers.php
@@ -475,7 +475,7 @@ $( document ).ready(function() {
                             }
                         }]
                 });
-            }, dataType="json");
+            }, "json");
         }
     });
 });
diff --git a/src/www/system_certmanager.php b/src/www/system_certmanager.php
index b8175ca65..72ac922ed 100644
--- a/src/www/system_certmanager.php
+++ b/src/www/system_certmanager.php
@@ -643,8 +643,8 @@ $( document ).ready(function() {
 //<![CDATA[
   function internalca_change() {
 
-    index = document.iform.caref.selectedIndex;
-    caref = document.iform.caref[index].value;
+    let index = document.iform.caref.selectedIndex;
+    let caref = document.iform.caref[index].value;
 
     switch (caref) {
   <?php
diff --git a/src/www/system_usermanager.php b/src/www/system_usermanager.php
index 3bae12e01..ffdd355fd 100644
--- a/src/www/system_usermanager.php
+++ b/src/www/system_usermanager.php
@@ -483,7 +483,7 @@ $( document ).ready(function() {
     // import ldap users
     $("#import_ldap_users").click(function(){
       event.preventDefault();
-      url="system_usermanager_import_ldap.php";
+      const url="system_usermanager_import_ldap.php";
       var oWin = window.open(url,"OPNsense","width=620,height=400,top=150,left=150,scrollbars=yes");
       if (oWin==null || typeof(oWin)=="undefined") {
         alert("<?= html_safe(gettext('Popup blocker detected. Action aborted.')) ?>");
@@ -497,7 +497,7 @@ $( document ).ready(function() {
         $.post(window.location, {act: 'newApiKey', userid: $("#userid").val() }, function(data) {
             if (data['key'] != undefined) {
                 // only generate a key file if there's data
-                output_data = 'key='+data['key'] +'\n' + 'secret='+data['secret'] +'\n';
+                const output_data = 'key='+data['key'] +'\n' + 'secret='+data['secret'] +'\n';
                 // create link, click and send to client
                 $('<a></a>')
                         .attr('id','downloadFile')
diff --git a/src/www/widgets/widgets/cpu_usage.widget.php b/src/www/widgets/widgets/cpu_usage.widget.php
index 1181980e3..9f32bf54b 100644
--- a/src/www/widgets/widgets/cpu_usage.widget.php
+++ b/src/www/widgets/widgets/cpu_usage.widget.php
@@ -52,7 +52,7 @@ require_once("system.inc");
       } else if (cpu_widget_cpu_data.length == 1) {
           cpu_widget_cpu_data.push([data['date_time'] * 1000, parseInt(data['cpu']['used'])]);
       }
-      chart_data = [];
+      let chart_data = [];
       cpu_widget_cpu_data.map(function(item){
           chart_data.push(item);
       });
diff --git a/src/www/widgets/widgets/gateways.widget.php b/src/www/widgets/widgets/gateways.widget.php
index b1d7f9e3f..48c7b6429 100644
--- a/src/www/widgets/widgets/gateways.widget.php
+++ b/src/www/widgets/widgets/gateways.widget.php
@@ -68,6 +68,7 @@ $gateways = return_gateways_array();
               $("#"+tr_id+" > td:eq(4)").html('<span>'+gateway['status_translated']+'</span>');
 
               // set color on status text
+              let status_color;
               switch (gateway['status']) {
                 case 'force_down':
                 case 'down':
@@ -81,7 +82,7 @@ $gateways = return_gateways_array();
                   status_color = 'success';
                   break;
                 default:
-                  status_color = 'default'
+                  status_color = 'default';
                   break;
               }
 
diff --git a/src/www/widgets/widgets/log.widget.php b/src/www/widgets/widgets/log.widget.php
index 3762da1f4..4433e781f 100644
--- a/src/www/widgets/widgets/log.widget.php
+++ b/src/www/widgets/widgets/log.widget.php
@@ -79,10 +79,10 @@ $nentriesinterfaces = isset($config['widgets']['filterlogentriesinterfaces']) ?
         // needed to display the widget settings menu
         $("#log-configure").removeClass("disabled");
         // icons
-        var field_type_icons = {'pass': 'fa-play', 'block': 'fa-ban'}
+        const field_type_icons = {'pass': 'fa-play', 'block': 'fa-ban'};
 
         var interface_descriptions = {};
-        ajaxGet(url='/api/diagnostics/interface/getInterfaceNames', {}, callback=function(data, status) {
+        ajaxGet('/api/diagnostics/interface/getInterfaceNames', {}, function(data, status) {
             interface_descriptions = data;
         });
         function fetch_log(){
@@ -95,7 +95,7 @@ $nentriesinterfaces = isset($config['widgets']['filterlogentriesinterfaces']) ?
                     'class': $(this).attr('class')
                 });
             });
-            ajaxGet(url='/api/diagnostics/firewall/log/', {'limit': 100}, callback=function(data, status) {
+            ajaxGet('/api/diagnostics/firewall/log/', {'limit': 100}, function(data, status) {
                 var filtact = [];
 
                 if ($("#actpass").is(':checked')) {
@@ -105,6 +105,7 @@ $nentriesinterfaces = isset($config['widgets']['filterlogentriesinterfaces']) ?
                     filtact.push('block');
                 }
 
+                let record;
                 while ((record=data.pop()) != null) {
                     var intf = record['interface'];
 
diff --git a/src/www/widgets/widgets/monit.widget.php b/src/www/widgets/widgets/monit.widget.php
index a34f3ecca..01621a96d 100644
--- a/src/www/widgets/widgets/monit.widget.php
+++ b/src/www/widgets/widgets/monit.widget.php
@@ -56,6 +56,7 @@ $( document ).ready(function() {
    ];
 
    // avoid running code twice due to <script> location within <body>
+
    if (typeof monitPollInit === 'undefined') {
       monitPollInit = false;
    } else {
@@ -64,7 +65,7 @@ $( document ).ready(function() {
 
    function monitStatusPoll() {
       var pollInterval = 10000;
-      ajaxCall(url="/api/monit/status/get/xml", sendData={}, callback=function(data, status) {
+      ajaxCall("/api/monit/status/get/xml", {}, function(data, status) {
          $("#grid-monit").bootgrid("clear");
          if (data['result'] === 'ok') {
             pollInterval = data['status']['server']['poll'] * 1000;
diff --git a/src/www/widgets/widgets/system_information.widget.php b/src/www/widgets/widgets/system_information.widget.php
index 49d824fd0..a6d7e4d92 100644
--- a/src/www/widgets/widgets/system_information.widget.php
+++ b/src/www/widgets/widgets/system_information.widget.php
@@ -52,8 +52,8 @@ require_once("system.inc");
       } else if (system_information_widget_cpu_data.length == 1) {
           system_information_widget_cpu_data.push(parseInt(data['cpu']['used']));
       }
-      chart_data = [];
-      count = 0;
+      let chart_data = [];
+      let count = 0;
       system_information_widget_cpu_data.map(function(item){
           chart_data.push([count, item]);
           count++;
@@ -114,7 +114,7 @@ require_once("system.inc");
       }
 
       // disk usage
-      counter = 0;
+      let counter = 0;
       $("#system_information_widget_disk .disk_devices").html("");
       data['disk']['devices'].map(function(device) {
           var html = $("#system_information_widget_disk .disk_template").html();
diff --git a/src/www/widgets/widgets/thermal_sensors.widget.php b/src/www/widgets/widgets/thermal_sensors.widget.php
index ac1c23aca..4bb227558 100644
--- a/src/www/widgets/widgets/thermal_sensors.widget.php
+++ b/src/www/widgets/widgets/thermal_sensors.widget.php
@@ -74,6 +74,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
           tr_content.push('</tr>');
           tbody.append(tr_content.join(''));
       }
+      let danger_temp, warning_temp;
       // probe warning / danger temp
       if (sensor['type'] == 'core') {
           danger_temp = parseInt($("#thermal_sensors_widget_core_critical_threshold").val());
diff --git a/src/www/widgets/widgets/traffic_graphs.widget.php b/src/www/widgets/widgets/traffic_graphs.widget.php
index 7a81126c6..182b4a5ac 100644
--- a/src/www/widgets/widgets/traffic_graphs.widget.php
+++ b/src/www/widgets/widgets/traffic_graphs.widget.php
@@ -52,9 +52,9 @@
           traffic_graph_widget_data.push(data);
       }
 
-      chart_data_in = [];
-      chart_data_out = [];
-      chart_data_keys = {};
+      let chart_data_in = [];
+      let chart_data_out = [];
+      let chart_data_keys = {};
       for (var i=traffic_graph_widget_data.length-1 ; i > 0 ; --i) {
           var elapsed_time = traffic_graph_widget_data[i]['time'] - traffic_graph_widget_data[i-1]['time'];
           for (var key in traffic_graph_widget_data[i]['interfaces']) {
@@ -67,6 +67,7 @@
                   chart_data_out[chart_data_out.length] = {'key': intf_item['name'], 'values': []};
               }
               if (chart_data_keys[key] != undefined) {
+                  let bps_in, bps_out;
                   if (elapsed_time > 0) {
                       bps_in = ((parseInt(intf_item['bytes received']) - parseInt(prev_intf_item['bytes received']))/elapsed_time)*8;
                       bps_out = ((parseInt(intf_item['bytes transmitted']) - parseInt(prev_intf_item['bytes transmitted']))/elapsed_time)*8;