index.js

module.exports.timer = (() => {
  let _timers = {};
  let _records = {};

  const _timer = (label = '_init', reset) => {
    if (!_timers[label] && !reset) {
      _timers[label] = process.hrtime();
      return;
    }
    if (reset) {
      delete _timers[label];
      _records[label] = [];
      _timers[label] = process.hrtime();
    }
    const hrtime = process.hrtime(_timers[label]);
    return Number((hrtime[0] + (hrtime[1] * 1e-9)).toPrecision(16));
  };
  const prettyPrint = (label, seconds) => {
    if (seconds < 1e-6) return label + ': ' + (seconds * 1e9) + ' ns';
    if (seconds < 1) return label + ': ' + (seconds * 1e3) + ' ms';
    return label + ': ' + seconds + ' s';
  };

  _timer.reset = () => {
    _timers = {};
    _labels = {};
  }

  _timer.start = (label) => _timer(label, true);

  _timer.end = (label) => {
    const seconds = _timer(label);
    _records[label] = _records[label] || [];
    _records[label].push(seconds);
    return seconds;
  };

  _timer.log = (label = "") => {
    if (!label) {
      console.log(_records);
      Object.keys(_records)
        .forEach(key => {
          console.log(
            prettyPrint(key, _records[key]
              .reduce((a, b) => a + b, 0) / _records[key].length
            )
          );
        });
      return;
    }
    const seconds = _timer(label);
    console.log(prettyPrint(label, seconds));
  };

  _timer.results = () => {
    return Object.keys(_records)
      .reduce((output, label) => {
        output[label] = _records[label]
          .reduce((a, b) => a + b, 0) / _records[label].length;
        return output;
      }, {});
  }
  return _timer;
})();