var isMatch = function(text, pattern, mem=new Map()) {
    let key = text + '__' + pattern, pLen = pattern.length,
        tLen = text.length, first_match;
    if (!mem.has(key)) {
        if (pLen === 0) {
            mem.set(key, tLen === 0);
            return tLen === 0;
        }
        first_match = (tLen !== 0 && (pattern[0] == text[0] ||
                       pattern[0] == '.'));
        if (pLen >= 2 && pattern[1] == '*'){
            mem.set(key, (isMatch(text, pattern.substring(2), mem) ||
                    (first_match && isMatch(text.substring(1), pattern, mem))));
        } else {
            mem.set(key, first_match && isMatch(text.substring(1),
                    pattern.substring(1), mem));
        }
    }
    return mem.get(key);
};