Updates to use __PREFIX__ template variable.

widget.html

<!-- wagtailleaflet/templates/leaflet/widget.html -->
{% load leaflet_tags %}
{% load static from staticfiles %}

<style type="text/css">{% block map_css %}
    {% if map_width and map_height %}#{{ id_map }} { width: {{ map_width }}; height: {{ map_height }}; }{% endif %}
    {% if not display_raw %}#{{ id }} { display: none; }{% endif %}
{% endblock map_css %}
</style>

<script type="text/javascript">
    {% block vars %}
        window.DEBUG_LEAFLET = true;
        window.DEBUG_LEAFLET && console.debug('widget.html : id_map = ' + '{{ id_map }}');
        window.LEAFLET_DATA = window.LEAFLET_DATA || {};
        window.LEAFLET_DATA['{{ id_map }}'] = {};
        window.LEAFLET_DATA['{{ id_map }}'].fieldid = '{{ id }}';
        window.LEAFLET_DATA['{{ id_map }}'].modifiable = {{ modifiable|yesno:"true,false" }};
        window.LEAFLET_DATA['{{ id_map }}'].geom_type = '{{ geom_type }}';
        window.LEAFLET_DATA['{{ id_map }}'].srid = {{ map_srid }};
    {% endblock vars %}

    window.LEAFLET_FUNCTIONS = window.LEAFLET_FUNCTIONS || {};
    window.LEAFLET_FUNCTIONS['{{ id_map }}'] = function(map, options) {
        window.LEAFLET_DATA['{{ id_map }}'].store_class = {{ field_store_class }};
        (new {{ geometry_field_class}}(window.LEAFLET_DATA['{{ id_map }}'])).addTo(map);
        {% block callback %}{% endblock callback %}
    };

    {% if target_map %}
        window.addEventListener('map:init', function (e) {
            var target_map = e.detail.map;
            target_map.on('map:loadfield', function (me) {
                if (me.fieldid == 'id_{{ target_map }}') {
                    setTimeout(function () {
                        window.LEAFLET_FUNCTIONS['{{ id_map }}'](target_map, e.detail.options);
                    }, 0);
                }
            });
        }, false);
    {% endif %}
</script>

{% if not target_map %}
    {% block map %}
        {% leaflet_map id_map callback=id_map_callback loadevent=loadevent settings_overrides=settings_overrides %}
    {% endblock map %}
{% endif %}

{% if display_raw %}<p> Geometry:</p>{% endif %}
<textarea id="{{ id }}" class="required" cols="150" rows="10" name="{{ name }}">{{ serialized }}</textarea>