将数字 12345678 转化成 RMB 形式 如： 12,345,678

let str = '1234132131232135678'
let tmp = [...str].reverse()
tmp = tmp
    .map((it, ind) =>
        ind % 3 === 0 ?
        [tmp[ind], tmp[ind + 1], tmp[ind + 2]]
        .reverse()
        .filter((it) => it !== undefined)
        .join('') :
        undefined
    )
    .filter((it) => it !== undefined)
    .reverse()
    .join(',')

console.log(tmp)