generate three characters timestamp that is sortable

three-characters-timestamp.ts

export function threeCharactersTimestamp(date?: Date) {
  if (!date) {
    date = new Date();
  }
  const [h, m, s] = [date.getHours(), date.getMinutes(), date.getSeconds()];

  // min & sec eatch 4 seconds
  const ms = Math.floor((m * 60 + s) / 4);
  const [m2, s2] = [Math.floor(ms / 30), ms % 30];

  // convert to three-characters-timestamp
  // l, 1 and 0 are not used to avoid confusing with i and o
  const lowers = [..."abcdefghijkmnopqrstuvwxyz"];
  const hChar = lowers[h];
  const alnum = [..."2345789", ...lowers.filter((c) => c != hChar)];
  const mChar = alnum[m2];
  const sChar = alnum.filter((c) => c != mChar)[s2];

  return date.toLocaleDateString("ja-JP", {
    year: "numeric",
    month: "2-digit",
    day: "2-digit",
  }).replaceAll("/", "") + "-" + hChar + mChar + sChar;
}

// console.log(threeCharactersTimestamp());
// -> generate current timestamp
// console.log(threeCharactersTimestamp(new Date('2022-05-01T10:33:22')));
// -> 20220501-kjq