Use external javascript file.


```ruby
TurnipFormatter::Template.add_js_file('http://example.com/turnip.min.js')
# =>
# <script src="http://example.com/turnip.min.js"></script>
#

TurnipFormatter::Template.add_js_file('./turnip.min.js')
# =>
# $(function() { alert('aaa'); });
#
```