Convert number of bytes into human readable format in JavaScript.

/**
 * Convert number of bytes into human readable format.
 *
 * @param integer bytes     Number of bytes to convert
 * @param integer precision Number of digits after the decimal separator
 * @return string
 */
function byteFormat(bytes, precision) {

  var isNumber = function (n) {
    return !isNaN(parseFloat(n)) && isFinite(n);
  };

  if (!isNumber(bytes)) {
    return "0 B";
  }

  var kilobyte = 1024,
      megabyte = kilobyte * 1024,
      gigabyte = megabyte * 1024,
      terabyte = gigabyte * 1024;

  if ((bytes >= 0) && (bytes < kilobyte)) {
    return bytes + ' B';

  } else if ((bytes >= kilobyte) && (bytes < megabyte)) {
    return (bytes / kilobyte).toFixed(precision) + ' KB';

  } else if ((bytes >= megabyte) && (bytes < gigabyte)) {
    return (bytes / megabyte).toFixed(precision) + ' MB';

  } else if ((bytes >= gigabyte) && (bytes < terabyte)) {
    return (bytes / gigabyte).toFixed(precision) + ' GB';

  } else if (bytes >= terabyte) {
    return (bytes / terabyte).toFixed(precision) + ' TB';

  } else {
    return bytes + ' B';
  }
}

// or

function byteFormat (bytes, precision) {
  var suffixes = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'],
    factor = Math.pow(10, precision > 0 ? precision : 2);

  for (var i = bytes, k = 0; i >= 1024 && k < suffixes.length; i /= 1024, k++) {}
  return (Math.round(i * factor) / factor) + ' ' + suffixes[k];
}
console.log(byteFormat(1024 * 1024 * 1024));