put queue in another module instead

for future reusability

scripts/common.js

@@ -0,0 +1,41 @@
+// common.js provides the advanced data structures. 
+
+export class Queue {
+     #elements;
+
+     constructor() {
+          this.#elements = [];
+     }
+
+     enqueue(element) {
+          this.#elements.push(element);
+     }
+
+     dequeue() {
+          return this.#elements.shift();
+     }
+
+     isEmpty() {
+          return this.#elements.length <= 0;
+     }
+}
+
+export class Stack {
+     #elements;
+
+     constructor() {
+          this.#elements = [];
+     }
+
+     push(element) {
+          this.#elements.push(element);
+     }
+
+     pop() {
+          return this.#elements.pop();
+     }
+
+     isEmpty() {
+          return this.#elements.length <= 0;
+     }
+}