Escape strings for JavaScript using Jinja2?

Jinja2 has nice filter tojson. If you make json from string, it will generate string enclosed in double quotes "". You can safely use it in javascript. And you don't need put quotes around by yourself.

$("#mydiv").append({{ html_string|tojson }});

It also escapes <>& symbols. So it is safe even when sting contains something XSS dangerous like <script>

This is a escapejs filter, based on Django's one, that I wrote for use in Jinja2 templates:

_js_escapes = {
        '\\': '\\u005C',
        '\'': '\\u0027',
        '"': '\\u0022',
        '>': '\\u003E',
        '<': '\\u003C',
        '&': '\\u0026',
        '=': '\\u003D',
        '-': '\\u002D',
        ';': '\\u003B',
        u'\u2028': '\\u2028',
        u'\u2029': '\\u2029'
}
# Escape every ASCII character with a value less than 32.
_js_escapes.update(('%c' % z, '\\u%04X' % z) for z in xrange(32))
def jinja2_escapejs_filter(value):
        retval = []
        for letter in value:
                if _js_escapes.has_key(letter):
                        retval.append(_js_escapes[letter])
                else:
                        retval.append(letter)

        return jinja2.Markup("".join(retval))
JINJA_ENVIRONMENT.filters['escapejs'] = jinja2_escapejs_filter

Example safe usage in a template:

<script type="text/javascript">
<!--
var variableName = "{{ variableName | escapejs }}";
…
//-->
</script>

When variableName is a str or unicode.