SOURCE

function deal(source) {
    let result = source.val;

    function find(node) {
        if (node.val > result) {
            result = node.val;
        }
        Object.keys(node).forEach(key => {
            if (typeof node[key] === 'object') {
                find(node[key]);
            }
        });
    }
    find(source);

    return result;
}

const data = {val: 1, b: {val: 2, b: {val: 1}, c: {val: 4}}};
console.log(deal(data));