parseDuration.ts

const SUFFIX_MULTIPLIER: Record<string, number> = {
  'ms': 1,
  's': 1000,
  'm': 60 * 1000,
  'h': 60 * 60 * 1000,
  'd': 24 * 60 * 60 * 1000,
  'w': 7 * 24 * 60 * 60 * 1000,
  'y': 365 * 24 * 60 * 60 * 1000,
}

const DURATION_REGEXP = new RegExp(
  /^(?:(?<value>\d+)(?<type>ms|s|m|h|d|w|y))|0$/i
);

function parseDuration(duration: string): number {
  let input = duration
  let parts: [number, string][] = [];

  function matchDuration(part: string) {
    const match = DURATION_REGEXP.exec(part);
    const hasValueAndType = Boolean(match?.groups?.value && match?.groups?.type)
    
    if (!match || !hasValueAndType) {
      throw new Error('not a valid duration')
    }

    if (match && hasValueAndType) {
      input = input.replace(match[0], '')
      parts.push([Number(match.groups.value), match.groups.type]);
    }

    if (input) {
      matchDuration(input);
    }
  }

  matchDuration(duration);
  
  if (!parts.length) {
    throw new Error('not a valid duration')
  }

  const totalDuration = parts.reduce((acc, [value, type]) => {
    const duration = value * SUFFIX_MULTIPLIER[type];
    return acc + duration;
  }, 0);

  return totalDuration;
}

parseDuration('2h45m'); // 9900000
parseDuration('2h'); // 7200000
parseDuration('30m'); // 1800000
parseDuration('1s'); // 1000
parseDuration('1d1d'); // 172800000

parseDuration('foo'); // this will throw