Make it possible to add objects to LinkedList.

src/data-structures/stack/Stack.js

@@ -18,11 +18,15 @@ export default class Stack {
   }
 
   push(value) {
-    this.linkedList.append({ value });
+    this.linkedList.append(value);
   }
 
   pop() {
     const removedTail = this.linkedList.deleteTail();
     return removedTail ? removedTail.value : null;
   }
+
+  toString(callback) {
+    return this.linkedList.toString(callback);
+  }
 }

src/data-structures/stack/__test__/Stack.test.js

@@ -13,7 +13,7 @@ describe('Stack', () => {
     stack.push(1);
     stack.push(2);
 
-    expect(stack.linkedList.toString()).toBe('1,2');
+    expect(stack.toString()).toBe('1,2');
   });
 
   it('should peek data from stack', () => {
@@ -49,4 +49,17 @@ describe('Stack', () => {
     expect(stack.pop()).toBeNull();
     expect(stack.isEmpty()).toBeTruthy();
   });
+
+  it('should be possible to push/pop objects', () => {
+    const stack = new Stack();
+
+    stack.push({ value: 'test1', key: 'key1' });
+    stack.push({ value: 'test2', key: 'key2' });
+
+    const stringifier = value => `${value.key}:${value.value}`;
+
+    expect(stack.toString(stringifier)).toBe('key1:test1,key2:test2');
+    expect(stack.pop().value).toBe('test2');
+    expect(stack.pop().value).toBe('test1');
+  });
 });