Looks like there is no JS version of BFS iterative yet...

```
var maxDepth = function(root) {
// iterative (BFS)
// http://stackoverflow.com/questions/1590247/how-do-you-implement-a-stack-and-a-queue-in-javascript
// algo book pdf p616
var queue = [];
queue.push(root);
var cur = {}; // tree node, object
var count = 0, size, i;
if (root !== null && root !== undefined) { // when root is null/undefined, return 0
while (queue.length > 0) {
// loop through all adjacent nodes of cur (binary tree, at most 2) --- from book
// let's record the size of queue for now, and after looping through all same-level nodes, count++
// this meets if there is only 1 root node as well
size = queue.length;
for (i = size; i > 0; i--) {
// dequeue, get the head of the node in queue out(FIFO)
cur = queue.shift();
if (cur.left !== null && cur.left !== undefined) {
queue.push(cur.left);
}
if (cur.right !== null && cur.right !== undefined) {
queue.push(cur.right);
}
}
count++; // same-level nodes all looped, count++
}
}
return count;
};
```