Use cursor with good old paginated web service

paginationToCursor.js

const get = require("./api")

const getAfter = async (limit, after) => {
  const vindex = parseInt(after.split(":")[0])

  const page = Math.floor(vindex / limit) + 1
  const modulo = vindex % limit

  const setId = page => (id, index) => {
    const vindex = (page - 1) * limit + index + 1
    return { id: `${vindex}:${id}` }
  }

  const format = (page, arg) => e => e.map(setId(page)).slice(...arg)
  const list = [[page, limit, [modulo]], [page + 1, limit, [0, modulo]]]

  const [r1, r2] = await Promise.all(
    list.map(([p, l, s]) => get(p, l).then(format(p, s)))
  )

  return [...r1, ...r2]
}
;(async () => {
  const r = await getAfter(3, "11:11")
  console.log(r)
})()