add statistic class

js/statistics.js

@@ -0,0 +1,23 @@
+class Stats {
+    #score;
+    #highScore;
+    #highScoreStorageKey;
+
+    constructor(highScoreStorageKey) {
+        // used as key for localStorage
+        
+        this.#highScoreStorageKey = highScoreStorageKey;
+
+        this.#score = 0;
+        this.#highScore = localStorage.getItem(this.#highScoreStorageKey) ?? 0;
+    }
+
+    incrementScore(value = 1) {
+        this.#score += value;
+
+        if (this.#highScore < this.#score) {
+            this.#highScore = this.#score;
+            localStorage.setItem(this.#highScoreStorageKey, this.#highScore);
+        }
+    }
+}