diff --git a/dev/js/src/api.js b/dev/js/src/api.js
index 059e638..8eeedf4 100644
--- a/dev/js/src/api.js
+++ b/dev/js/src/api.js
@@ -1,34 +1,35 @@
 define(['util'], function () {
-  // TODO: https://github.com/honza/140medley/blob/master/140medley.js
-  // https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
-  // https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest
-  // r.addEventListener("progress", updateProgress, false);
-  // http://www.javascriptkit.com/javatutors/loadjavascriptcss.shtml
-  // http://stackoverflow.com/questions/6112744/load-javascript-on-demand
+  "use strict";
+
+  // TODO:
+  // - https://github.com/honza/140medley/blob/master/140medley.js
+  // - https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
+  // - https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest
+  // - r.addEventListener("progress", updateProgress, false);
+  // - http://www.javascriptkit.com/javatutors/loadjavascriptcss.shtml
+  // - http://stackoverflow.com/questions/6112744/load-javascript-on-demand
 
   KorAP.URL = KorAP.URL !== undefined ? KorAP.URL : '';
-
   KorAP.API = KorAP.API || {};
 
+  const legacySigle = new RegExp('^([^_]+)_([^\\.]+)\\.(.+?)$');
+
   /**
    * Retrieve information about a match
    */
   KorAP.API.getMatchInfo = function (match, param, cb) {
 
     // match is a KorAP.Match object
-    var url = KorAP.URL;
-    url += '/corpus';
+    let url = KorAP.URL + '/corpus';
     /*
       url += '/' + match.corpusID;
       url += '/' + match.docID;
       url += '/' + match.textID;
     */
 
-    var legacySigle = new RegExp('^([^_]+)_([^\\.]+)\\.(.+?)$');
-
     // This is for legacy support
-    var legacy = legacySigle.exec(match.textSigle);
-    var docFragment = "";
+    const legacy = legacySigle.exec(match.textSigle);
+    let docFragment = "";
     if (legacy !== null && legacy[0]) {
       docFragment = legacy[1] + '/' + legacy[2] + '/' + legacy[3];
     }
@@ -70,9 +71,7 @@
   KorAP.API.getTextInfo = function (doc, param, cb) {
 
     // doc is a KorAP.Match object
-    var url = KorAP.URL;
-    url += '/corpus';
-    url += '/' + doc.textSigle;
+    let url = KorAP.URL + '/corpus' + '/' + doc.textSigle;
 
     if (param['fields'] !== undefined) {
       url += '?fields='; // TODO!
@@ -80,6 +79,7 @@
     else {
       url += '?fields=@all'; // TODO: Maybe '*'?
     }
+
     KorAP.API.getJSON(url, cb, "TextInfo: " + doc.textSigle);
   };
 
@@ -91,24 +91,6 @@
     KorAP.API.getJSON(KorAP.URL + '/collection', cb, "CorpusInfo");
   };
 
-
-  /**
-   * Retrieve information about corpus statistic
-   * 
-   * Development mode:
-   * URL = http://localhost:8089/api 
-   * 
-   * collectionQuery has be changed to corpusQuery 
-   */
-  /* KorAP.API.getCorpStat = function (collQu, cb){
-  	//development mode:
-  	var url = "http://localhost:8089/api/";
-  	url  = url + "statistics";
-  	url = url + "?cq=";
-  	url = url + collQu;
-  	KorAP.API.getJSON(url, cb);
-  };*/
-
   
   /**
    * Retrieve information about corpus statistic
@@ -121,20 +103,20 @@
    * http://localhost:3000/corpus?cq=availability+%3D+%2FCC-BY.*%2F+%26+textClass+%3D+%22kultur%22
    */
   KorAP.API.getCorpStat = function (cq, cb){
-  	var url  =  KorAP.URL;
-    url += "/corpus?cq=" + encodeURIComponent(cq);
+  	let url  =  KorAP.URL + "/corpus?cq=" + encodeURIComponent(cq);
   	KorAP.API.getJSON(url, cb, "CorpusInfo: " + cq);
   };
   
+
   /**
    * General method to retrieve JSON information
    */
   KorAP.API.getJSON = function (url, onload, title) {
-    var req = new XMLHttpRequest();
+    const req = new XMLHttpRequest();
     req.open("GET", url, true);
 
     // Dispatch global "window" event
-    var reqE = new CustomEvent('korapRequest', {
+    const reqE = new CustomEvent('korapRequest', {
       bubbles : false,
       detail: {
         "url" : url,
@@ -156,7 +138,7 @@
       */
       if (this.readyState == 4) {
 
-        var json;
+        let json;
         try {
           json = JSON.parse(this.responseText);
         }
@@ -166,11 +148,13 @@
           onload(undefined);
           return;
         };
+
 	      if (json !== undefined && json["errors"] !== undefined) {
 	        json["errors"].forEach(
             e => KorAP.log(e[0], e[1] || "Unknown")
 	        );
 	      }
+
         else if (this.status !== 200) {
         	KorAP.log(this.status, this.statusText);
         };
@@ -178,11 +162,13 @@
 	      if (this.status === 200) {
 	        onload(json);
 	      }
+
 	      else {
           onload(undefined);
         };
       }
     };
+
     req.ontimeout = function () {
       KorAP.log(0, 'Request Timeout');
     };
diff --git a/dev/js/src/buttongroup.js b/dev/js/src/buttongroup.js
index 29453c3..7c8d8c6 100644
--- a/dev/js/src/buttongroup.js
+++ b/dev/js/src/buttongroup.js
@@ -11,8 +11,8 @@
     
     // Initialize button group
     _init : function (classes) {
-      var e = document.createElement('div');
-      var cl = e.classList;
+      const e = document.createElement('div');
+      const cl = e.classList;
       if (classes) {
         cl.add.apply(cl,classes);
       };
@@ -51,7 +51,7 @@
      */
     add : function (title, data, cb) {
       
-      var b = this._element.addE('span');
+      const b = this._element.addE('span');
       b.setAttribute('title',title);
 
       if (data !== undefined) {
@@ -70,14 +70,14 @@
      
       b.addE('span').addT(title);
 
-      var that = this;
+      let that = this;
       b.addEventListener('click', function (e) {
 
         // Do not bubble
         e.halt();
         
         // Call callback
-        var obj = that._bind || this;
+        let obj = that._bind || this;
         obj.button = b;
         cb.apply(obj, e)
       });
@@ -92,13 +92,12 @@
      * Returns the list object.
      */
     addList : function (title, data, itemClass = defaultItemClass) {
-      var list = treeMenuClass.create([], itemClass);
+      const list = treeMenuClass.create([], itemClass);
       this.add(title, data, function (e) {
         list.show();
         list.button(this.button);
         list.focus();
       });
-
       return list;
     },
 
@@ -107,17 +106,20 @@
      * The state has to be a state object.
      */
     addToggle : function (title, data, state) {
-      let b = this._element.addE('span');
+      const b = this._element.addE('span');
       b.setAttribute('title',title);
 
       if (data != undefined) {
         if (data['cls'] !== undefined) {
-          b.classList.add.apply(b.classList, data['cls']);
+          b.classList.add.apply(
+            b.classList,
+            data['cls']
+          );
         };
       };
 
       // Set check marker
-      let check = b.addE('span');
+      const check = b.addE('span');
       check.classList.add("check", "button-icon");
       check.addE('span');
 
diff --git a/dev/js/src/buttongroup/menu.js b/dev/js/src/buttongroup/menu.js
index bebaac4..3ee7ec3 100644
--- a/dev/js/src/buttongroup/menu.js
+++ b/dev/js/src/buttongroup/menu.js
@@ -16,12 +16,12 @@
      *   as an array of arrays.
      */
     create : function (list, itemClass) {
-      var obj = Object.create(menuClass)
-	        .upgradeTo(this)
-	        ._init(list, {itemClass : itemClass});
+      const obj = Object.create(menuClass)
+	          .upgradeTo(this)
+	          ._init(list, {itemClass : itemClass});
       obj.limit(6);
 
-      var e = obj.element();
+      const e = obj.element();
 
       // This is only domspecific
       e.addEventListener('blur', function (e) {
@@ -36,6 +36,7 @@
       return obj;
     },
 
+
     /**
      * The panel object of the menu.
      */
@@ -46,12 +47,12 @@
       return this._panel;
     },
 
+
     // Attach menu to button
     button : function (btn) {
 
       this._button = btn;
 
-      // this._attached = e;
       this._repos(this._button);
       this.slider().reInit();
 
@@ -70,7 +71,7 @@
       window.addEventListener('scroll', this._onscroll);
     },
 
-
+    
     // Overwrite onHide method
     onHide : function () {
 
@@ -82,7 +83,7 @@
     },
 
     _repos : function (e) {
-      var bounding = e.getBoundingClientRect();
+      const bounding = e.getBoundingClientRect();
       this._element.style.left = bounding.left + "px";
       this._element.style.top = (
         bounding.top +