dead simple calculator for time

time-calculator.html

<textarea id=input style="width: 50%; height: 5em; white-space: pre" oninput="result.innerText = calculate(this.value)"></textarea>
<div id=result></div>
<script>
  window.onload = () => {
    input.value = '1d 2h 3m 4s + 4h 5s - 2030s + 28h';
    input.dispatchEvent(new Event('input')) 
  };
  function calculate(input) { 
    const units = Object.entries({ d: 86400, h: 3600, m: 60, s: 1 }); 
    const seconds = eval(
      input.replace(
        /[\d\w\s]+/g,
        x => '(' + units.reduce((acc, unit) => acc.replace(new RegExp('(\\d+)' + unit[0]), '+$1*' + unit[1]), x) + ')'
      )
    );
    const result = units.reduce(
      ([result, reminder], unit) => [result + Math.floor(reminder / unit[1]) + unit[0] + ' ', reminder % unit[1]], ['', seconds]
    )[0];
    return result + '\n' + units.map(unit => (seconds / unit[1]) + ' ' + unit[0]).join('\n'); 
  }
</script>