react-number-format/custom_formatters/card_expiry.js

React component to format number in an input or as a text.

/**
 *  This method limit val between 1 to max
 *  val and max both are passed as string
 **/
function limit(val, max) {
  if (val.length === 1 && val[0] > max[0]) {
    val = '0' + val;
  }

  if (val.length === 2) {
    if (Number(val) === 0) {
      val = '01';

    //this can happen when user paste number
  } else if (val > max) {
      val = max;
    }
  }

  return val;
}

export function cardExpiry(val) {
  const month = limit(val.substring(0, 2), '12');
  const year = val.substring(2, 4);

  return month + (year.length ? '/' + year : '');
}