function balancedParentesis(string) {
  return !string.split("").reduce(function(previous, char) {
    if (previous < 0) return previous;
    if (char === "(") return previous + 1;
    if (char === ")") return previous - 1;
    return previous;
  }, 0);
}

balancedParentesis("))(("); // False
balancedParentesis(")"); // False
balancedParentesis("()"); // True