mask.js

// Mask('**.**.****', '17.02');
// Mask('+7 (***) ***-**-**', '9854554354123283293');
// Mask('+7 (***) ***-**-**', '9854554354123283293', { isStrict: true });
export function mask(maskStr, str, { isStrict = false } = {}) {
  let decorSymbCount = 0;
  let maskedStr = '';

  for (let i = 0; i < maskStr.length && str[i - decorSymbCount]; i++) {
    const m = maskStr[i];
    const v = str[i - decorSymbCount];

    if (m !== '*') {
      maskedStr += m;
      if (str[i] !== m) decorSymbCount++;
      continue;
    }

    maskedStr += v;
  }

  if (isStrict) return maskedStr;

  const starsCount = maskStr.split('').filter(m => m === '*').length;

  return `${maskedStr}${str.slice(starsCount)}`;
}

// unmask('**.**.****', '16.03.2020');
export function unmask(maskStr, str) {
  let unmaskedStr = '';

  for (let i = 0; i < maskStr.length && str[i]; i++) {
    if (maskStr[i] === '*') unmaskedStr += str[i];
  }

  return unmaskedStr;
}