Merge pull request #8 from truck-js/feature/to-array-callback

feat: add callback to `toArray` method

README.md

@@ -67,6 +67,11 @@ determine whether the `value` matches.
 
 **O(n)**. Converts the _Singly Linked-List_'s values to an array.
 
+### `toArray(callback: (node: Node) => any): any[]`
+
+**O(n)**. Converts the _Singly Linked-List_ to an array, the `callback` receives the `Node` with
+each iteration.
+
 ## Properties
 
 ### `.length: number`

src/index.js

@@ -2,6 +2,7 @@ import isFunction from 'lodash.isfunction';
 
 import Node from './node';
 
+const defaultCallback = a => a.value;
 const defaultComparator = a => b => a === b;
 
 class SinglyLinkedList {
@@ -106,11 +107,11 @@ class SinglyLinkedList {
     return undefined;
   }
 
-  toArray() {
+  toArray(callback = defaultCallback) {
     const returnArray = [];
     let current = this.head;
     while (current) {
-      returnArray.push(current.value);
+      returnArray.push(callback(current));
       current = current.next;
     }
     return returnArray;

src/index.test.js

@@ -357,17 +357,26 @@ describe('.toArray()', () => {
     expect(singlyLinkedList.toArray()).toEqual([]);
   });
 
-  test('Returns an array of items inside the SinglyLinkedList', () => {
-    const VALUE_A = 'VALUE_A';
-    const VALUE_B = 'VALUE_B';
-    const VALUE_C = 'VALUE_C';
-    const expected = [VALUE_A, VALUE_B, VALUE_C];
+  describe('After values have been inserted', () => {
+    beforeAll(() => {
+      singlyLinkedList.insert(1);
+      singlyLinkedList.insert(2);
+      singlyLinkedList.insert(3);
+      singlyLinkedList.insert(4);
+      singlyLinkedList.insert(5);
+    });
 
-    singlyLinkedList.insert(VALUE_C);
-    singlyLinkedList.insert(VALUE_B);
-    singlyLinkedList.insert(VALUE_A);
-    const actual = singlyLinkedList.toArray();
+    test('Returns an array of items inside the SinglyLinkedList', () => {
+      expect(singlyLinkedList.toArray()).toEqual([5, 4, 3, 2, 1]);
+    });
 
-    expect(actual).toEqual(expected);
+    test('Can be used as a \'map\' method if passed a callback', () => {
+      const callback = node => (node.value + ((node.next && node.next.value) || 0));
+      const expected = [9, 7, 5, 3, 1];
+
+      const actual = singlyLinkedList.toArray(callback);
+
+      expect(actual).toEqual(expected);
+    });
   });
 });