vendors/tempy.js/toMaxLen
    var toMaxLen = (input, maxLength) => {
      let negative = input[0] === "-" ? "-" : "";
      if (negative) {
        input = input.slice(1);
        maxLength--;
      }
      while (input.length < maxLength)
        input = "0" + input;
      return negative ? "-" + input : input;
    };