turns a byte count into an object which can be used to compose KB/MB/GB/TB/PB values

getBytes.js

const getBytes = (bytes,{unit=null,binary=false,toFixed=1} = {}) => {
  const divisor = binary?1024:1000;
  let value = bytes;
  let sizeLevel=-1;
  const sizeArray=['KB','MB','GB','TB','PB'];
  if(unit){
    sizeLevel=sizeArray.indexOf(unit);
    value=(bytes/Math.pow(divisor,sizeLevel+1)).toFixed(toFixed)
  }
  else while(value>=divisor){
    value=(value/divisor);
    if(value<100)value=value.toFixed(toFixed);
    else value=Math.floor(value);
    sizeLevel++;
  }
  if(sizeLevel<0)value = (value/divisor).toFixed(toFixed);
  return {bytes,value,unit:sizeArray[sizeLevel]||'KB'};
}

// Returned object can be composed into a string like `${Number(obj.value).toLocaleString()} ${obj.unit}`