credit card formatter

format-cc.js

const blocks = {
  uatp:          [4, 5, 6],
  amex:          [4, 6, 5],
  diners:        [4, 6, 4],
  discover:      [4, 4, 4, 4],
  mastercard:    [4, 4, 4, 4],
  dankort:       [4, 4, 4, 4],
  instapayment:  [4, 4, 4, 4],
  jcb15:         [4, 6, 5],
  jcb:           [4, 4, 4, 4],
  maestro:       [4, 4, 4, 4],
  visa:          [4, 4, 4, 4],
  mir:           [4, 4, 4, 4],
  unionPay:      [4, 4, 4, 4],
  general:       [4, 4, 4, 4],
  generalStrict: [4, 4, 4, 7]
}

const patterns = {
  // starts with 1; 15 digits, not starts with 1800 (jcb card)
  uatp: /^(?!1800)1\d{0,14}/,

  // starts with 34/37; 15 digits
  amex: /^3[47]\d{0,13}/,

  // starts with 6011/65/644-649; 16 digits
  discover: /^(?:6011|65\d{0,2}|64[4-9]\d?)\d{0,12}/,

  // starts with 300-305/309 or 36/38/39; 14 digits
  diners: /^3(?:0([0-5]|9)|[689]\d?)\d{0,11}/,

  // starts with 51-55/2221–2720; 16 digits
  mastercard: /^(5[1-5]\d{0,2}|22[2-9]\d{0,1}|2[3-7]\d{0,2})\d{0,12}/,

  // starts with 5019/4175/4571; 16 digits
  dankort: /^(5019|4175|4571)\d{0,12}/,

  // starts with 637-639; 16 digits
  instapayment: /^63[7-9]\d{0,13}/,

  // starts with 2131/1800; 15 digits
  jcb15: /^(?:2131|1800)\d{0,11}/,

  // starts with 2131/1800/35; 16 digits
  jcb: /^(?:35\d{0,2})\d{0,12}/,

  // starts with 50/56-58/6304/67; 16 digits
  maestro: /^(?:5[0678]\d{0,2}|6304|67\d{0,2})\d{0,12}/,

  // starts with 22; 16 digits
  mir: /^220[0-4]\d{0,12}/,

  // starts with 4; 16 digits
  visa: /^4\d{0,15}/,

  // starts with 62; 16 digits
  unionPay: /^62\d{0,14}/
}

export default function formatCc(value) {
  var block
  for (var key in patterns) {
    if (patterns[key].test(value)) {
      block = blocks[key]
    }
  }

  if (!block) {
    return value
  }

  let result = ''
  let currentDelimiter = ' '

  block.forEach((length, index) => {
    if (value.length > 0) {
      let sub = value.slice(0, length)
      let rest = value.slice(length)

      result += sub

      if (sub.length === length && index < block.length - 1) {
        result += currentDelimiter
      }

      // update remaining string
      value = rest
    }
  })

  return result
}