Add topological sorting.

src/data-structures/stack/Stack.js

@@ -5,10 +5,16 @@ export default class Stack {
     this.linkedList = new LinkedList();
   }
 
+  /**
+   * @return {boolean}
+   */
   isEmpty() {
     return !this.linkedList.tail;
   }
 
+  /**
+   * @return {LinkedListNode}
+   */
   peek() {
     if (!this.linkedList.tail) {
       return null;
@@ -17,15 +23,35 @@ export default class Stack {
     return this.linkedList.tail.value;
   }
 
+  /**
+   * @param {*} value
+   */
   push(value) {
     this.linkedList.append(value);
   }
 
+  /**
+   * @return {LinkedListNode}
+   */
   pop() {
     const removedTail = this.linkedList.deleteTail();
     return removedTail ? removedTail.value : null;
   }
 
+  /**
+   * @return {*[]}
+   */
+  toArray() {
+    return this.linkedList
+      .toArray()
+      .map(linkedListNode => linkedListNode.value)
+      .reverse();
+  }
+
+  /**
+   * @param {function} [callback]
+   * @return {string}
+   */
   toString(callback) {
     return this.linkedList.toString(callback);
   }

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

@@ -62,4 +62,16 @@ describe('Stack', () => {
     expect(stack.pop().value).toBe('test2');
     expect(stack.pop().value).toBe('test1');
   });
+
+  it('should be possible to convert stack to array', () => {
+    const stack = new Stack();
+
+    expect(stack.peek()).toBeNull();
+
+    stack.push(1);
+    stack.push(2);
+    stack.push(3);
+
+    expect(stack.toArray()).toEqual([3, 2, 1]);
+  });
 });