Mastering Flask Web Development - Second Edition

The tojson filter

We use the tojson filter to pass the variable to the Python json.dumps function, as shown in the following code. Remember that your passed object must be serializable by the json module:

{{ {'key': False, 'key2': None, 'key3': 45} | tojson }} 
{key: false, key2: null, key3: 45} 

This feature is most commonly used to pass SQLAlchemy models to JavaScript MVC frameworks upon the loading of the page load than waiting for an AJAX request. If you use tojson in this way, remember to pass the result to the safe filter as well to make sure that you don't get HTML escape sequences in your JavaScript. Here is an example with a collection of models from Backbone.js, a popular JavaScript MVC framework:

var collection = new PostCollection({{ ...