Simple & elegant file size formatter

formatSizeSI.js

#!/usr/bin/env node
require('v8').setFlagsFromString('--harmony_destructuring');
const assert = require('assert');

function formatSizeSI(size) {
  var index = Math.floor(Math.log(Math.abs(size)) / Math.log(1000)) | 0;
  return +(size / Math.pow(1000, index)).toPrecision(3) + ' '
    + (index ? 'kMGTPEZY'[--index] + 'B' : 'Bytes');
}

[
  [-5678000, '-5.68 MB'],
  [-1, '-1 Bytes'],
  [0, '0 Bytes'],
  [1, '1 Bytes'],
  [1234, '1.23 kB'],
  [5678000, '5.68 MB'],
  [80000001, '80 MB'],
  [80060001, '80.1 MB'],
  [180560001, '181 MB'],
  [80000000000, '80 GB'],
  ['foo', 'NaN Bytes'],
].forEach(([actual, expected]) => assert.equal(formatSizeSI(actual), expected));