javascript - Converting file size in bytes to human-readable string

Question

I'm using this function to convert a file size in bytes to a human-readable file size:

function getReadableFileSizeString(fileSizeInBytes) {
    var i = -1;
    var byteUnits = [' kB', ' MB', ' GB', ' TB', 'PB', 'EB', 'ZB', 'YB'];
    do {
        fileSizeInBytes = fileSizeInBytes / 1024;
        i++;
    } while (fileSizeInBytes > 1024);

    return Math.max(fileSizeInBytes, 0.1).toFixed(1) + byteUnits[i];
};

However, it seems like this isn't 100% accurate. For example:

getReadableFileSizeString(1551859712); // output is "1.4 GB"

Shouldn't this be "1.5 GB"? It seems like the division by 1024 is losing precision. Am I totally misunderstanding something or is there a better way to do this?

Answer 1

Here's one I wrote:

/**
 * Format bytes as human-readable text.
 * 
 * @param bytes Number of bytes.
 * @param si True to use metric (SI) units, aka powers of 1000. False to use 
 *           binary (IEC), aka powers of 1024.
 * @param dp Number of decimal places to display.
 * 
 * @return Formatted string.
 */
function humanFileSize(bytes, si=false, dp=1) {
  const thresh = si ? 1000 : 1024;

  if (Math.abs(bytes) < thresh) {
    return bytes + ' B';
  }

  const units = si 
    ? ['kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'] 
    : ['KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB'];
  let u = -1;
  const r = 10**dp;

  do {
    bytes /= thresh;
    ++u;
  } while (Math.round(Math.abs(bytes) * r) / r >= thresh && u < units.length - 1);


  return bytes.toFixed(dp) + ' ' + units[u];
}


console.log(humanFileSize(1551859712))  // 1.4 GiB
console.log(humanFileSize(5000, true))  // 5.0 kB
console.log(humanFileSize(5000, false))  // 4.9 KiB
console.log(humanFileSize(-10000000000000000000000000000))  // -8271.8 YiB
console.log(humanFileSize(999949, true))  // 999.9 kB
console.log(humanFileSize(999950, true))  // 1.0 MB
console.log(humanFileSize(999950, true, 2))  // 999.95 kB
console.log(humanFileSize(999500, true, 0))  // 1 MB