@@ -0,0 +1,92 @@
+'use strict';
+
+class Cache {
+constructor() {
+const proto = Object.getOf(this);
+if (proto.constructor === Cache) {
+throw new Error('Abstract class should not be instanciated');
+}
+this.allocated = 0;
+}
+
+read(key) {
+const s = JSON.stringify({ read: { key } });
+throw new Error('Method is not implemented: ' + s);
+}
+
+add(key, val) {
+const s = JSON.stringify({ add: { key, val } });
+throw new Error('Method is not implemented: ' + s);
+}
+
+delete(key) {
+const s = JSON.stringify({ delete: { key } });
+throw new Error('Method is not implemented: ' + s);
+}
+}
+
+class MapCache extends Cache {
+constructor() {
+super();
+this.data = new Map();
+}
+
+read(key) {
+return this.data.get(key);
+}
+
+add(key, val) {
+const prev = this.data.get(key);
+if (prev) this.allocated -= prev.length;
+this.allocated += val.length;
+this.data.set(key, val);
+}
+
+delete(key) {
+const val = this.data.get(key);
+if (val) {
+this.allocated -= val.length;
+this.data.delete(key);
+}
+}
+}
+
+class ObjectCache extends Cache {
+constructor() {
+super();
+this.data = {};
+}
+
+read(key) {
+return this.data[key];
+}
+
+add(key, val) {
+const prev = this.data[key];
+if (prev) this.allocated -= prev.length;
+this.allocated += val.length;
+this.data[key] = val;
+}
+
+delete(key) {
+const val = this.data[key];
+if (val) {
+this.allocated -= val.length;
+delete this.data[key];
+}
+}
+}
+
+// Usage
+
+const mapCache = new MapCache();
+mapCache.add('key1', 'value1');
+mapCache.add('key2', 'value2');
+mapCache.delete('key2');
+console.dir(mapCache);
+
+const objCache = new ObjectCache();
+objCache.add('key1', 'value1');
+objCache.add('key2', 'value2');
+objCache.delete('key2');
+console.dir(objCache);