const vs var

const.fn.js

const limit = getLimit(query.limit)
const after = getAfter(query.after)

// after must be a unix timestamp number or Date string
function getAfter (after) {
  after = new Date(/^([0-9]+)$/.test(after) ? Number(after) * 1000 : after)
  return after.valueOf() ? after : new Date()
}

// limit must be a number between 0 and 100
function getLimit (limit) {
  limit = /^([0-9]{1,3})$/.test(limit) ? Number(limit) : 20
  return limit < 0 || limit > 100 ? 20 : limit
}

const.js

// limit must be a number between 0 and 100
const limit = (limit => {
  limit = /^([0-9]{1,3})$/.test(limit) ? Number(limit) : 20
  return limit < 0 || limit > 100 ? 20 : limit
})(query.limit)

// after must be a unix timestamp number or Date string
const after = (after => {
  after = new Date(/^([0-9]+)$/.test(after) ? Number(after) * 1000 : after)
  return after.valueOf() ? after : new Date()
})(query.after)

var.js

// limit must be a number between 0 and 100
var limit = /^([0-9]{1,3})$/.test(query.limit) ? Number(query.limit) : 20
limit = limit < 0 || limit > 100 ? 20 : limit

// after must be a unix timestamp number or Date string
var after = new Date(/^([0-9]+)$/.test(query.after) ? Number(query.after) * 1000 : query.after)
after = after.valueOf() ? after : new Date()