function findByQuery(query) {
    let i, results = [];
    for (i in window.localStorage) {
        if (window.localStorage.hasOwnProperty(i)) {
            if (i.match(query) || (!query && typeof i === 'string')) {
                results.push(i);
            }
        }
    }
    return results;
}

console.log(findByQuery('test'));