Flatten a tree into an array by combining the keys.

flatten_tree.js

// Flatten a tree into an array by combining the keys.
var flatten_tree = function(obj) {
    var sep = '/';
    var ret = [];
    function _flat(elem, base) {
        base = ((base === undefined) ? '' : base + sep);
        for (let i in elem){
            if (!elem.hasOwnProperty(i)) continue;

            let val = elem[i];
            if ((typeof val) === 'object') {
                if (_.isEmpty(val)) {
                    ret.push(base + i);
                } else {
                    _flat(elem[i], base + i);
                }
            }
        }
        return ret;
    }
    return _flat(obj);
}