JavaScript で数字を漢数字に変換する例

111011101110 を "一一一〇一一一〇一一一〇" ではなく "千百十億千百十万千百十" とするタイプです。

toKanjiNumber.js

const kanjiNumeral = [
  // これ以上は Number.MAX_SAFE_INTEGER を超えるため考慮しない。
  [1000000000000, "兆"],
  [100000000, "億"],
  [10000, "万"],
  [1000, "千"],
  [100, "百"],
  [10, "十"],
];

const kanjiDigits = ["", "一", "二", "三", "四", "五", "六", "七", "八", "九"];

const kanjiRecursive = (value) => {
  let current = value;
  let str = "";

  kanjiNumeral.forEach(([base, char]) => {
    const num = Math.floor(current / base);

    if (!num) return;

    let recurredStr = kanjiRecursive(num);

    if ("千百十".includes(char) && recurredStr.endsWith("一")) {
      recurredStr = str.substring(0, recurredStr.length - 1);
    }

    current -= num * base;

    str = `${str}${recurredStr}${char}`;
  });

  return `${str}${kanjiDigits[current]}`;
};

const toKanjiNumber = (value) => {
  let num = Number(value);

  if (num === 0) return "〇";

  let positive = true;

  if (num < 0) {
    positive = false;
    num = Math.abs(num);
  }

  const str = kanjiRecursive(num);

  return positive ? str : `-${str}`;
};

export default toKanjiNumber;