Depth-First and Breadth-First In JS

dfs_bfs.js

function depthFirst(root) {
    // initialize the stack with the root node
    let stack = [root];

    // continue running the algorithm while there are still nodes on the stack
    while (stack.length) {

        // pop the top node from the stack
        let node = stack.pop();

        // we consider a node visited once we pop it,
        // so we should print the node's value now
        console.log(node.val);

        // add the node's left and right children, if they exist
        if (node.right) stack.push(node.right);
        if (node.left) stack.push(node.left);

        // IMPORTANT: do not print out the children yet; they must wait their turn to be popped first
    }
}

function breadthFirst(root) {
    // initialize the queue with the root node
    let queue = [root];

    // continue running the algorithm while there are still nodes on the queue
    while (queue.length) {
        // remove the front node from the queue
        let node = queue.shift();

        // the node we just removed is now "visited", so print it
        console.log(node.val);

        // add the left and right children to the back of the queue, if they exist
        if (node.left) queue.push(node.left);
        if (node.right) queue.push(node.right);

        // IMPORTANT: do not print out the children yet; they must wait their turn to exit the front of the queue first
    }
}

tree_node.js

class TreeNode {
    constructor(val) {
        this.val = val;
        this.left = null;
        this.right = null;
    }
}

let a = new TreeNode('a');
let b = new TreeNode('b');
let c = new TreeNode('c');
let d = new TreeNode('d');
let e = new TreeNode('e');
let f = new TreeNode('f');

a.left = b;
a.right = c;
b.left = d;
b.right = e;
c.right = f;