Flatten a nested array and combine/crawl by a specified property

flatten-by-prop.js

/**
 * Flatten a nested array and combine/crawl by specified property
 */
flattenByProp (arr, prop) {
    var flatten = function (arr) {
        return arr.reduce(function (flat, toFlatten) {

            // combine items on this level
            var combo = flat.concat(toFlatten);

            // if categories are array,
            if(Array.isArray(toFlatten[prop])){
                return combo.concat(flatten(toFlatten[prop]));
            }else{
                return combo;
            }
        }, []);
    };

    return flatten(arr);
}