fix some bugs. need to continue bug testing.

javascript/lru_cache.js

@@ -0,0 +1,52 @@
+const LRU_CACHE_MAX_ITEMS_DEFAULT = 250;
+class LRUCache {
+    /** Least Recently Used cache implementation.
+     * 
+     *  Source: https://stackoverflow.com/a/46432113
+    */
+    constructor(max = LRU_CACHE_MAX_ITEMS_DEFAULT) {
+        isNumberThrowError(max);
+
+        this.max = max;
+        this.cache = new Map();
+    }
+
+    clear() {
+        this.cache.clear();
+    }
+
+    destroy() {
+        this.clear();
+        this.cache = null;
+    }
+
+    size() {
+        return this.cache.size;
+    }
+
+    get(key) {
+        let item = this.cache.get(key);
+        if (!isNullOrUndefined(item)) {
+            this.cache.delete(key);
+            this.cache.set(key, item);
+        }
+        return item;
+    }
+
+    set(key, val) {
+        if (this.cache.has(key)) {
+            this.cache.delete(key);
+        } else if (this.cache.size === this.max) {
+            this.cache.delete(this.first());
+        }
+        this.cache.set(key, val);
+    }
+
+    has(key) {
+        return this.cache.has(key);
+    }
+
+    first() {
+        return this.cache.keys().next().value;
+    }
+}