In Chrome 31 on Mavericks, `(new Intl.NumberFormat()).format(3500);` returns `"3,500"`

It doesn't throw an error, it uses the default locale based on the environment.

`(new Intl.NumberFormat()).resolvedOptions();` returns:
```
{
  locale: "en-US",
  maximumFractionDigits: 3,
  minimumFractionDigits: 0,
  minimumIntegerDigits: 1,
  numberingSystem: "latn",
  style: "decimal",
  useGrouping: true
}
```