This won't work because the spec requires a `currency` value when the `{style: 'currency'}`, e.g.:

```js
var nf = new Intl.NumberFormat('en-US', {
  style: 'currency',
  currency: 'USD'
});
```

Also in the template the `BOOKS_ON` message isn't even being used. This should be updated to make sure that it is.