function toBytes(size, type)

{

  const types = ["B", "KB", "MB", "GB", "TB"];

​

  const key = types.indexOf(type.toUpperCase())

  if (typeof key !== "boolean") {

      return  size * Math.pow(1024, key);

  }

  return "invalid type: type must be GB/KB/MB etc.";

}

​

console.log(toBytes(5, 'GB'))