treeCountLeaves

var Tree = function(value) {
  this.value = value;
  this.children = [];
};

Tree.prototype.countLeaves = function() {
  let count = 0;
  const countChildren = node => {
    if (node.children.length === 0) {
      count++;
      return;
    }
    for (let i = 0; i < node.children.length; i++) {
      countChildren(node.children[i]);
    }
  };
  countChildren(this);
  return count;
};

/**
 * You shouldn't need to change anything below here, but feel free to look.
 */

/**
 * add an immediate child
 * (wrap values in Tree nodes if they're not already)
 */
Tree.prototype.addChild = function(child) {
  if (!child || !(child instanceof Tree)) {
    child = new Tree(child);
  }

  if (!this.isDescendant(child)) {
    this.children.push(child);
  } else {
    throw new Error("That child is already a child of this tree");
  }
  // return the new child node for convenience
  return child;
};

/**
 * check to see if the provided tree is already a child of this
 * tree __or any of its sub trees__
 */
Tree.prototype.isDescendant = function(child) {
  if (this.children.indexOf(child) !== -1) {
    // `child` is an immediate child of this tree
    return true;
  } else {
    for (var i = 0; i < this.children.length; i++) {
      if (this.children[i].isDescendant(child)) {
        // `child` is descendant of this tree
        return true;
      }
    }
    return false;
  }
};

/**
 * remove an immediate child
 */
Tree.prototype.removeChild = function(child) {
  var index = this.children.indexOf(child);
  if (index !== -1) {
    // remove the child
    this.children.splice(index, 1);
  } else {
    throw new Error("That node is not an immediate child of this tree");
  }
};