Convert bytes to formatted KB, MB, GB, TB, etc. in JavaScript.

formatBytes.html

<pre id=o></pre>
<script>
const UNITS = ",K,M,G,T,P".split(",");
const UNIT_SIZES = UNITS.reduce((prev, curr, i) => {
  prev[curr] = Math.pow(1024, i);
  return prev;
}, {});

const formatBytes = bytes => {
  let size, unit;
  for (let i = UNITS.length - 1; i >= 0; i--) {
    unit = UNITS[i];
    size = UNIT_SIZES[unit];
    if (bytes >= size) {
      return (Math.round(bytes / size * 100) / 100).toLocaleString("en-US") + ` ${unit}B`;
    }
  }
  return 0;
};



//Demonstrate its usage:
const DEMO = [223,1234,1234567,1234567890,1234567890000,1234567890000000];

o.innerHTML = DEMO.map(a => `${formatBytes(a)} (${a.toLocaleString("en-US")} bytes)`).join("\n");
</script>