Create getters and setters for meta data in binary tree node.

src/data-structures/tree/BinaryTreeNode.js

@@ -5,7 +5,7 @@ export default class BinaryTreeNode {
    * @param {*} [value] - node value.
    * @param {Object} meta - any meta information that needs to be attached to the node.
    */
-  constructor(value = null, meta = null) {
+  constructor(value = null, meta = {}) {
     this.left = null;
     this.right = null;
     this.parent = null;
@@ -157,6 +157,29 @@ export default class BinaryTreeNode {
     return traverse;
   }
 
+  /**
+   * @param {string} property
+   * @param {*} value
+   * @return {BinaryTreeNode}
+   */
+  setMeta(property, value) {
+    this.meta[property] = value;
+
+    return this;
+  }
+
+  /**
+   * @param property
+   * @return {*}
+   */
+  getMeta(property) {
+    if (!this.meta || !Object.prototype.hasOwnProperty.call(this.meta, property)) {
+      return null;
+    }
+
+    return this.meta[property];
+  }
+
   /**
    * @return {string}
    */

src/data-structures/tree/__test__/BinaryTreeNode.test.js

@@ -204,4 +204,23 @@ describe('BinaryTreeNode', () => {
     expect(redNode.meta.color).toBe('red');
     expect(blackNode.meta.color).toBe('black');
   });
+
+  it('should be possible to use get/set methods to change node meta information', () => {
+    const redNode = new BinaryTreeNode(1, { color: 'red' });
+    const blackNode = new BinaryTreeNode(2, { color: 'black' });
+
+    expect(redNode.getMeta('color')).toBe('red');
+    expect(blackNode.getMeta('color')).toBe('black');
+
+    redNode.setMeta('size', 8);
+
+    expect(redNode.getMeta('size')).toBe(8);
+    expect(redNode.getMeta('color')).toBe('red');
+    expect(redNode.getMeta('not_existing')).toBeNull();
+
+    // It must also be possible to override meta information.
+    redNode.setMeta('color', 'blue');
+    expect(redNode.getMeta('size')).toBe(8);
+    expect(redNode.getMeta('color')).toBe('blue');
+  });
 });