Vue.js cast as json not working

Whats the syntax to cast data to json in vue.js

I've been trying to follow the laracast episode http://ift.tt/1IeM5eS where the data is cast to json using:

 <pre>
            {{ $data | json }}
 </pre>

However I get the following error: Use of undefined constant json - assumed 'json'

I'm using Vue.js v1.0.13, the one in the episode is an older version but I can't seem to find the correct syntax?

via Chebli Mohamed