Format file size like macOS

format-size.js

function formatSize(size) {
  const base = 1000; // 1000 or 1024
  const kb = base ** 1;
  const mb = base ** 2;
  const gb = base ** 3;
  let num;

  num = (size / 1).toFixed(0);
  if (num < base) return Number(num) + ' B';

  num = (size / kb).toFixed(0);
  if (num < base) return Number(num) + ' KB';

  num = (size / mb).toFixed(1);
  if (num < base) return Number(num) + ' MB';

  num = (size / gb).toFixed(2);
  if (num < base) return Number(num) + ' GB';

  return Number(num) + ' GB+';
}