Given a elapsed time in milliseconds and an optional precision returns a formatted string in the form of Xh Ym Zs

formattedElapsedTime.js

/*
  example:

  const startTime = Date.now();
  ... some long computation ... 
  const elapsedInMS = Date.now() - startTime;
  
  console.log(formattedElapsedTime(elapsedInMS, 3));
*/

const formattedElapsedTime = (elapsedInMS, precision) => {
  precision = precision || 2;

  const secondsInMS = 1000;
  const minutesInMS = secondsInMS * 60;
  const hoursInMS = minutesInMS * 60;

  let remainingInMS = elapsedInMS;

  const hours = Math.floor(remainingInMS / hoursInMS);
  remainingInMS -= (hours * hoursInMS)

  const minutes = Math.floor(remainingInMS / minutesInMS);
  remainingInMS -= (minutes * minutesInMS)

  const seconds = remainingInMS / secondsInMS;

  const result = [];
  if (hours > 0) {
    result.push(`${hours.toFixed(precision)}h`);
  }
  if (minutes > 0) {
    result.push(`${minutes.toFixed(precision)}m`);
  }
  result.push(`${seconds.toFixed(precision)}s`);

  return result.join(" ");
};