Kilo.js

/*
  Kilo.js
  #toSize: 2048 => "2 KB"
  #toBytes: "2 KB" => 2048
*/
var Kilo = (function() {
  "use strict";
  var kilo = 1024;
  var sizes = { "B": 0, "KB": 1, "MB": 2, "GB": 3, "TB": 4 };
  var sizesNames = Object.keys(sizes);
  var rSize = /(\d+)\s*(B|KB|MB|GB|TB)*/i;
  function isNaN(value) {
	return value !== value;
  };
  return {
    // Based on: http://scratch99.com/web-development/javascript/convert-bytes-to-mb-kb/
    toSize: function(bytes, digits, separator) {
      var isNegative = false;
      if (bytes === 0 || isNaN(bytes)) return 'n/a';
      if (bytes < 0) isNegative = true, bytes *= -1;
      var i = Number(Math.floor(Math.log(bytes) / Math.log(kilo)));
      bytes = i === 0 ? bytes : (bytes / Math.pow(kilo, i)).toFixed(digits >= 0 ? digits : 2);
      return (isNegative ? "-" : "") + [bytes, sizesNames[i]].join(typeof separator === "string" ? separator : " ");
    },
    toBytes: function(size, unit) {
      var match = rSize.exec(size);
      return !match ? NaN : Number(match[1]) * (match[2] ? Math.pow(kilo, sizes[match[2].toUpperCase()]) : 1);
    }
  };
}());

function toSize(bytes, digits, separator) {
  return Kilo.toSize(bytes, digits, separator);
}