Update step2-04 exercises

step2-04/exercise/src/stack.spec.ts

@@ -1,15 +1,17 @@
-describe('stack', () => {
+// Import the stack here
+
+describe('Stack', () => {
   it('should push item to the top of the stack', () => {
     // implement test here:
-    // 1. require the stack
-    // 2. create stack push calls to place some items in the stack
-    // 3. write assertions via the expect() API
+    // 1. Create a stack instance
+    // 2. Use stack push calls to add some items to the stack
+    // 3. Write assertions via the expect() API
   });
 
   it('should pop the item from the top of stack', () => {
     // implement test here:
-    // 1. require the stack
-    // 2. create stack push calls to place some items in the stack
+    // 1. Create a stack instance
+    // 2. Use stack push calls to add some items to the stack
     // 3. pop a few items off the stack
     // 4. write assertions via the expect() API
   });

step2-04/exercise/src/stack.ts

@@ -1,13 +1,27 @@
 export class Stack<T> {
   private _items: T[] = [];
 
+  /** Add an item to the top of the stack. */
   push(item: T) {
     this._items.push(item);
   }
 
+  /** Remove the top item from the stack and return it. */
   pop(): T {
     if (this._items.length > 0) {
       return this._items.pop();
     }
   }
+
+  /** Return the top item from the stack without removing it. */
+  peek(): T {
+    if (this._items.length > 0) {
+      return this._items[this._items.length - 1];
+    }
+  }
+
+  /** Get the number of items in the stack/ */
+  get count(): number {
+    return this._items.length;
+  }
 }