code: function encodeNumber_(num) {
    let encodedNumber = '';
    while (num >= 0x20) {
      encodedNumber += CHAR64_.charAt(
        0x20 | (num & 0x1f));
      num >>= 5;
    }
    encodedNumber += CHAR64_.charAt(num);
    return encodedNumber;
  }
docs: Transform a number into a logical sequence of characters.
  @param {number} num Number.
  @return {string} String.
  @private
  @hidden