Code style fixes.

src/data-structures/tree/BinaryTreeNode.js

@@ -2,8 +2,8 @@ import Comparator from '../../utils/comparator/Comparator';
 
 export default class BinaryTreeNode {
   /**
-   * @param {*} value
-   * @param {BinaryTreeNode} parent
+   * @param {*} [value]
+   * @param {BinaryTreeNode} [parent]
    */
   constructor(value = null, parent = null) {
     this.left = null;

src/data-structures/tree/binary-search-tree/BinarySearchTree.js

@@ -1,8 +1,12 @@
 import BinarySearchTreeNode from './BinarySearchTreeNode';
 
 export default class BinarySearchTree {
-  constructor() {
-    this.root = new BinarySearchTreeNode();
+  /**
+   * @param {function} [nodeValueCompareFunction]
+   */
+  constructor(nodeValueCompareFunction) {
+    this.nodeValueCompareFunction = nodeValueCompareFunction;
+    this.root = new BinarySearchTreeNode(null, null, this.nodeValueCompareFunction);
   }
 
   /**

src/data-structures/tree/binary-search-tree/BinarySearchTreeNode.js

@@ -3,14 +3,15 @@ import Comparator from '../../../utils/comparator/Comparator';
 
 export default class BinarySearchTreeNode extends BinaryTreeNode {
   /**
-   * @param {*} value
-   * @param {BinaryTreeNode} parent
-   * @param {function} compareFunction
+   * @param {*} [value]
+   * @param {BinaryTreeNode} [parent]
+   * @param {function} [compareFunction]
    */
   constructor(value = null, parent = null, compareFunction = undefined) {
     super(value, parent);
 
     // This comparator is used to compare node values with each other.
+    this.compareFunction = compareFunction;
     this.nodeValueComparator = new Comparator(compareFunction);
   }
 
@@ -29,14 +30,14 @@ export default class BinarySearchTreeNode extends BinaryTreeNode {
       if (this.left) {
         this.left.insert(value);
       } else {
-        this.setLeft(new BinarySearchTreeNode(value));
+        this.setLeft(new BinarySearchTreeNode(value, null, this.compareFunction));
       }
     } else if (this.nodeValueComparator.greaterThan(value, this.value)) {
       // Insert to the right.
       if (this.right) {
         this.right.insert(value);
       } else {
-        this.setRight(new BinarySearchTreeNode(value));
+        this.setRight(new BinarySearchTreeNode(value, null, this.compareFunction));
       }
     }
 

src/data-structures/tree/binary-search-tree/__test__/BinarySearchTree.test.js

@@ -46,4 +46,29 @@ describe('BinarySearchTree', () => {
     bst.remove(20);
     expect(bst.toString()).toBe('10');
   });
+
+  it('should insert object values', () => {
+    const nodeValueComparatorCallback = (a, b) => {
+      const normalizedA = a || { value: null };
+      const normalizedB = b || { value: null };
+
+      if (normalizedA.value === normalizedB.value) {
+        return 0;
+      }
+
+      return normalizedA.value < normalizedB.value ? -1 : 1;
+    };
+
+    const obj1 = { key: 'obj1', value: 1, toString: () => 'obj1' };
+    const obj2 = { key: 'obj2', value: 2, toString: () => 'obj2' };
+    const obj3 = { key: 'obj3', value: 3, toString: () => 'obj3' };
+
+    const bst = new BinarySearchTree(nodeValueComparatorCallback);
+
+    bst.insert(obj2);
+    bst.insert(obj3);
+    bst.insert(obj1);
+
+    expect(bst.toString()).toBe('obj1,obj2,obj3');
+  });
 });