diff --git a/umap/static/umap/js/umap.controls.js b/umap/static/umap/js/umap.controls.js
index 34a380ea..0985cd5c 100644
--- a/umap/static/umap/js/umap.controls.js
+++ b/umap/static/umap/js/umap.controls.js
@@ -880,7 +880,7 @@ L.U.Map.include({
       })
     }
 
-    var filterFeatures = function () {
+    const filterFeatures = function () {
       let noResults = true
       this.eachDataLayer((datalayer) => {
         datalayer.eachFeature(function (feature) {
diff --git a/umap/static/umap/js/umap.features.js b/umap/static/umap/js/umap.features.js
index 2fac5fca..32460d97 100644
--- a/umap/static/umap/js/umap.features.js
+++ b/umap/static/umap/js/umap.features.js
@@ -140,7 +140,7 @@ L.U.FeatureMixin = {
 
   appendEditFieldsets: function (container) {
     const optionsFields = this.getShapeOptions()
-    var builder = new L.U.FormBuilder(this, optionsFields, {
+    let builder = new L.U.FormBuilder(this, optionsFields, {
       id: 'umap-feature-shape-properties',
       callback: this._redraw,
     })
@@ -148,7 +148,7 @@ L.U.FeatureMixin = {
     shapeProperties.appendChild(builder.build())
 
     const advancedOptions = this.getAdvancedOptions()
-    var builder = new L.U.FormBuilder(this, advancedOptions, {
+    builder = new L.U.FormBuilder(this, advancedOptions, {
       id: 'umap-feature-advanced-properties',
       callback: this._redraw,
     })
diff --git a/umap/static/umap/js/umap.js b/umap/static/umap/js/umap.js
index 7af18388..6ac6690f 100644
--- a/umap/static/umap/js/umap.js
+++ b/umap/static/umap/js/umap.js
@@ -340,7 +340,7 @@ L.U.Map.include({
       'umap-slideshow-enabled',
       this.options.slideshow && this.options.slideshow.active
     )
-    for (var i in this._controls) {
+    for (const i in this._controls) {
       this.removeControl(this._controls[i])
     }
     if (this.options.noControl) return
@@ -357,7 +357,7 @@ L.U.Map.include({
       })
     }
     let name, status, control
-    for (var i = 0; i < this.HIDDABLE_CONTROLS.length; i++) {
+    for (let i = 0; i < this.HIDDABLE_CONTROLS.length; i++) {
       name = this.HIDDABLE_CONTROLS[i]
       status = this.options[name + 'Control']
       if (status === false) continue
@@ -846,7 +846,7 @@ L.U.Map.include({
     L.DomEvent.on(
       download,
       'click',
-      function () {
+      () => {
         const type = types[typeInput.value]
         const content = type.formatter(this)
         let name = this.options.name || 'data'
@@ -957,7 +957,7 @@ L.U.Map.include({
       if (layerId) layer = map.datalayers[layerId]
       if (layer && clearFlag.checked) layer.empty()
       if (fileInput.files.length) {
-        var file
+        let file
         for (let i = 0, file; (file = fileInput.files[i]); i++) {
           type = type || L.Util.detectFileType(file)
           if (!type) {
diff --git a/umap/static/umap/js/umap.layer.js b/umap/static/umap/js/umap.layer.js
index 1da7fdde..2113ea15 100644
--- a/umap/static/umap/js/umap.layer.js
+++ b/umap/static/umap/js/umap.layer.js
@@ -644,7 +644,7 @@ L.U.DataLayer = L.Evented.extend({
 
   _polygonToLayer: function (geojson, latlngs) {
     // Ensure no empty hole
-    // for (var i = latlngs.length - 1; i > 0; i--) {
+    // for (let i = latlngs.length - 1; i > 0; i--) {
     //     if (!latlngs.slice()[i].length) latlngs.splice(i, 1);
     // }
     return new L.U.Polygon(this.map, latlngs, { geojson: geojson, datalayer: this })
@@ -984,14 +984,12 @@ L.U.DataLayer = L.Evented.extend({
       L.DomEvent.on(a, 'click', L.DomEvent.stop).on(
         a,
         'click',
-        function () {
-          this.restore(data.name)
-        },
+        () => this.restore(data.name),
         this
       )
     }
 
-    var versionsContainer = L.DomUtil.createFieldset(container, L._('Versions'), {
+    const versionsContainer = L.DomUtil.createFieldset(container, L._('Versions'), {
       callback: function () {
         this.map.xhr.get(this.getVersionsUrl(), {
           callback: function (data) {
@@ -1073,8 +1071,8 @@ L.U.DataLayer = L.Evented.extend({
   },
 
   getNextFeature: function (feature) {
-    const id = this._index.indexOf(L.stamp(feature)),
-      nextId = this._index[id + 1]
+    const id = this._index.indexOf(L.stamp(feature))
+    const nextId = this._index[id + 1]
     return nextId ? this._layers[nextId] : this.getNextBrowsable().getFeatureByIndex(0)
   },
 
@@ -1082,8 +1080,8 @@ L.U.DataLayer = L.Evented.extend({
     if (this._index <= 1) {
       return null
     }
-    const id = this._index.indexOf(L.stamp(feature)),
-      previousId = this._index[id - 1]
+    const id = this._index.indexOf(L.stamp(feature))
+    const previousId = this._index[id - 1]
     return previousId
       ? this._layers[previousId]
       : this.getPreviousBrowsable().getFeatureByIndex(-1)
diff --git a/umap/static/umap/js/umap.slideshow.js b/umap/static/umap/js/umap.slideshow.js
index b03ac6fe..f353cc54 100644
--- a/umap/static/umap/js/umap.slideshow.js
+++ b/umap/static/umap/js/umap.slideshow.js
@@ -13,8 +13,8 @@ L.U.Slideshow = L.Class.extend({
     this.map = map
     this._id = null
 
-    let // current feature
-      current = null
+    // current feature
+    let current = null
 
     const self = this
     try {
diff --git a/umap/static/umap/js/umap.ui.js b/umap/static/umap/js/umap.ui.js
index 39416f2e..73158257 100644
--- a/umap/static/umap/js/umap.ui.js
+++ b/umap/static/umap/js/umap.ui.js
@@ -85,7 +85,7 @@ L.U.UI = L.Evented.extend({
     this._alert.innerHTML = ''
     L.DomUtil.addClass(this.parent, 'umap-alert')
     L.DomUtil.addClass(this._alert, level_class)
-    const close = function () {
+    function close() {
       if (timeoutID !== this.ALERT_ID) {
         return
       } // Another alert has been forced
diff --git a/umap/templates/umap/locale.js b/umap/templates/umap/locale.js
index 374a6206..7dcf434b 100644
--- a/umap/templates/umap/locale.js
+++ b/umap/templates/umap/locale.js
@@ -1,3 +1,3 @@
-var locale = {{ locale|safe }};
-L.registerLocale("{{ locale_code }}", locale);
-L.setLocale("{{ locale_code }}");
\ No newline at end of file
+const locale = {{ locale|safe }}
+L.registerLocale("{{ locale_code }}", locale)
+L.setLocale("{{ locale_code }}")