Wagtail Markdown - simplest way

markdownblock.py

# django
from django import forms
from django.contrib.staticfiles.templatetags.staticfiles import static
from django.forms import Media, widgets
from django.utils.functional import cached_property

# wagtail
from wagtail.utils.widgets import WidgetWithScript
from wagtail.wagtailcore import blocks

# markdown
import markdown as MarkdownLibrary


class MarkdownBlock(blocks.TextBlock):

    @cached_property
    def field(self):
        field_kwargs = {
            'widget': MarkdownWidget(),
        }
        field_kwargs.update(self.field_options)
        return forms.CharField(**field_kwargs)

    class Meta:
        icon = 'code'
        template = 'blocks/markdown.html'


class MarkdownWidget(WidgetWithScript, widgets.Textarea):

    def render_js_init(self, id_, name, value):
        jsinit = """
            if (window.SimpleMDEInstances == null) {{
                window.SimpleMDEInstances = [];
            }}
            sm = new SimpleMDE({{
                element: document.getElementById("{id!s}"),
                forceSync: true,
                spellChecker: false
            }});
            window.SimpleMDEInstances.push(sm);
        """
        return jsinit.format(id=id_)

    @property
    def media(self):
        js = [
            static('simplemde/js/simplemde.min.js'),
        ]
        css = {'all': [
            static('simplemde/css/simplemde.min.css'),
        ]}

        return Media(js=js, css=css)

templatetag_markdown.py

# django
from django import template
from django.utils.safestring import mark_safe

# markdown
import markdown as MarkdownLibrary


register = template.Library()


@register.filter(name='markdown')
def markdown_filter(value):
    return mark_safe(MarkdownLibrary.markdown(
        value,
        output_format='html5',
    ))

SimpleMDE required - it can be downloaded here: https://simplemde.com/