http://plnkr.co/edit/bB1m5UOpLJJUIlHOYKAO?p=preview

For very large numbers when converting to a string the browser might use the "#e#" format which breaks the use of appending "e"+fractionSize and produces NaN.

The MDN page that formatNumber references appears to handle this by doing a .split('e') before generating the "#e#" string: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round