Traverse binary tree using a generator function and an iterator.

binaryTree.js

class BinaryTree {

   constructor(value, left = null, right = null) {
      this.value = value;
      this.left = left;
      this.right = right;
   }

   * [Symbol.iterator]() {
      yield this.value;

      if (this.left) {
         yield* this.left;
      } 

      if (this.right) {
         yield* this.right;
      }
   }

}

/* Create a tree

           a
         /   \
       b       e
      / \     
     c   d   
  
*/

let node1 = new BinaryTree('e');
let node2 = new BinaryTree('c');
let node3 = new BinaryTree('d');
let node4 = new BinaryTree('b', node2, node3);
let tree = new BinaryTree('a', node4, node1);

// Iterate over the tree and print the values
for (let value of tree) {
   console.log(value);
}

// Output:
// a
// b
// c
// d
// e