Your [Sinatra](http://sinatrarb.com) app:
```ruby
get '/' do
callback = params.delete('callback') # jsonp
json = {'your' => 'data'}.to_json
if callback
content_type :js
response = "#{callback}(#{json})"
else
content_type :json
response = json
end
response
end
```
Your HTML:
```ruby
```
You can also do the same with jQuery:
```ruby
$.ajax({
type: 'get',
url: '/',
dataType: 'jsonp',
success: function(data) {
parseResponse(data);
}
})
```