diff --git a/README.md b/README.md
index 886f2dd..569e33a 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,10 @@ In this way contextual search <a href="https://rawgit.com/nextapps-de/flexsearch
 
 __Note:__ This feature is actually not enabled by default.
 
+###### TF-IDF / BM25?
+
+> "TF-IDF and all kinds of variations (like BM25) is a big mistake in searching algorithm today. They does'nt provide either: a meaningful relevance of a term as well as the importance of it! Like many pseudo-intelligent algorithm this is also an example of mathematical stupidity." — Thomas Wilkerling, _Contextual-based Scoring_, 2018
+
 <a name="webworker"></a>
 #### Web-Worker Support
 
diff --git a/flexsearch.js b/flexsearch.js
index 9f9429a..4ef0b01 100644
--- a/flexsearch.js
+++ b/flexsearch.js
@@ -316,18 +316,6 @@ var SUPPORT_ASYNC = true;
 
                                 if(self._current_callback && (self._task_completed === self.worker)){
 
-                                    // if(typeof self._last_empty_query !== 'undefined'){
-                                    //
-                                    //     if(self._task_result.length){
-                                    //
-                                    //         self._last_empty_query = "";
-                                    //     }
-                                    //     else{
-                                    //
-                                    //         self._last_empty_query || (self._last_empty_query = query);
-                                    //     }
-                                    // }
-
                                     // store result to cache
 
                                     if(self.cache){
@@ -447,11 +435,6 @@ var SUPPORT_ASYNC = true;
             this._timer = null;
             this._status = true;
 
-            // if(this.mode === 'forward' || this.mode === 'reverse' || this.mode === 'both'){
-            //
-            //     this._last_empty_query = "";
-            // }
-
             if(SUPPORT_CACHE) {
 
                 this.cache = custom = (
@@ -951,11 +934,6 @@ var SUPPORT_ASYNC = true;
 
                 if(SUPPORT_CACHE && this.cache){
 
-                    // if(typeof this._last_empty_query !== 'undefined'){
-                    //
-                    //     this._last_empty_query = "";
-                    // }
-
                     this._cache.reset();
                 }
 
@@ -974,13 +952,6 @@ var SUPPORT_ASYNC = true;
                 }
             }
 
-            // validate last query
-
-            // else if((typeof this._last_empty_query !== 'undefined') && this._last_empty_query && (query.indexOf(this._last_empty_query) === 0)){
-            //
-            //     return result;
-            // }
-
             // encode string
 
             _query = this.encode(/** @type {string} */ (_query));
@@ -1082,6 +1053,7 @@ var SUPPORT_ASYNC = true;
 
                                 count > 1 ?
 
+                                    // https://jsperf.com/merge-arrays-comparison
                                     check.concat.apply([], map_check)
                                 :
                                     map_check[0]
@@ -1114,18 +1086,6 @@ var SUPPORT_ASYNC = true;
                 //result = intersect_3d(check, limit, this.suggest);
             }
 
-            // if(typeof this._last_empty_query !== 'undefined'){
-            //
-            //     if(result.length){
-            //
-            //         this._last_empty_query = "";
-            //     }
-            //     else{
-            //
-            //         this._last_empty_query || (this._last_empty_query = query);
-            //     }
-            // }
-
             // store result to cache
 
             if(SUPPORT_CACHE && this.cache){
@@ -2252,9 +2212,11 @@ var SUPPORT_ASYNC = true;
             }
             else if(length_z){
 
-                result = result.concat.apply(result, arrays[0]);
+                arrays = arrays[0];
 
-                if(limit && result && (result.length > limit)){
+                result = arrays.length > 1 ? result.concat.apply(result, arrays) : arrays[0];
+
+                if(limit && (result.length > limit)){
 
                     // Note: do not touch original array!
 
@@ -2274,6 +2236,7 @@ var SUPPORT_ASYNC = true;
          * @returns {Array}
          */
 
+        /*
         function intersect_sorted(a, b, limit){
 
             var result = [];
@@ -2319,6 +2282,7 @@ var SUPPORT_ASYNC = true;
 
             return result;
         }
+        */
 
         /**
          * @param {FlexSearch} ref
diff --git a/package.json b/package.json
index aa2e69a..9c092e1 100644
--- a/package.json
+++ b/package.json
@@ -52,10 +52,10 @@
     "chai": "^4.1.2",
     "coveralls": "^3.0.0",
     "google-closure-compiler": "^20180402.0.0",
-    "mocha": "^5.0.5",
+    "mocha": "^5.1.1",
     "mocha-lcov-reporter": "^1.3.0",
     "mocha-phantomjs": "^4.1.0",
-    "nyc": "^11.6.0",
+    "nyc": "^11.7.1",
     "phantomjs-prebuilt": "^2.1.16",
     "updtr": "^2.0.0"
   }