doing step 4 demo notes

step2-04/exercise/src/stack.ts

@@ -1 +1,13 @@
-// Place your implementation from Step 2-01 exercise here
+export class Stack<T> {
+  private _items: T[] = [];
+
+  push(item: T) {
+    this._items.push(item);
+  }
+
+  pop(): T {
+    if (this._items.length > 0) {
+      return this._items.pop();
+    }
+  }
+}