数字に千・万・億などの日本語の桁を付けるJS

num2ja.js

/**
 * 数字に漢字の桁を付ける
 * ex: 1234567890123 => 1兆2345億6789万123
 * @param {String | Number} num 数字
 * @return {String} 漢字付きの数字
 */
export default function num2ja(num) {
  const keta = ['', '千', '万', '億', '兆']

  let jaNum = ''
  let count = 0

  num = String(num).replace(',', '')

  // 千
  if(num.length <= 3) {
    return num
  }
  else {
    const n = num.slice(-3) - 0 + ''
    jaNum = [n !== '0' ? `${n}${keta[count]}` : '', jaNum].join('')
    num = (num / 1000 | 0) + ''
    count++
  }
  // 万
  if(num.length > 1) {
    const n = num.slice(-1) - 0 + ''
    jaNum = [n !== '0' ? `${n}${keta[count]}` : '', jaNum].join('')
    num = (num / 10 | 0) + ''
    count++
  }
  // それ以降
  while(num.length > 4) {
    const n = num.slice(-4) - 0 + ''
    jaNum = [n !== '0' ? `${n}${keta[count]}` : '', jaNum].join('')
    num = (num / 10000 | 0) + ''
    count++
  }
  jaNum = [num !== '0' ? `${num}${keta[count]}` : '', jaNum].join('')
  return jaNum
}