Safely JSON-encode objects in your Django template

json.py

from django.core.serializers.json import DjangoJSONEncoder
from django.template import Library
from json import dumps as json_dumps

register = Library()


@register.filter
def json(data):
    """
    Safely JSON-encode an object.

    To protect against XSS attacks, HTML special characters (<, >, &) and unicode newlines
    are replaced by escaped unicode characters. Django does not escape these characters
    by default.

    Output of this method is not marked as HTML safe. If you use it inside an HTML
    attribute, it must be escaped like regular data:

    <div data-user="{{ data|json }}">

    If you use it inside a <script> tag, then the output does not need to be escaped,
    so you can mark it as safe:

    <script>
    var user = {{ data|json|safe }};
    </script>

    Escaped characters taken from Rails json_escape() helper:
    https://github.com/rails/rails/blob/v4.2.5/activesupport/lib/active_support/core_ext/string/output_safety.rb#L60-L113
    """
    unsafe_chars = {
        '&': '\\u0026',
        '<': '\\u003c',
        '>': '\\u003e',
        '\u2028': '\\u2028',
        '\u2029': '\\u2029'}
    json_str = json_dumps(data, cls=DjangoJSONEncoder)

    for (c, d) in unsafe_chars.items():
        json_str = json_str.replace(c, d)

    return json_str

@amacneil – thanks for contributing this. I was just looking to do the same thing & that saves the trouble. What license are you releasing this under – the same as Django core?

@amacneil I'd like to get this change applied to the Django-jsonify package, would you be happy for me to make a PR based on this gist? https://bitbucket.org/marltu/django-jsonify