Edit in JSFiddle

can.Component.extend({
    tag: 'x-markdown',
    template: '<div class="markdown" style="display:none;"><content/></div><div>{{{html}}}</div>',
    scope: {
        html: can.compute(function() {
            var markdown = this.attr('markdown');
            var converter = new Showdown.converter();
            var html = converter.makeHtml(markdown);
            return html;
        }),
        markdown: ''
    },
    events: {
        'inserted': function(el) {
            var content = el.find('.markdown').html();
            this.scope.attr('markdown', content);
        },
        
    }
});

$('#main').html(can.view('my-prose', {}));

<div id="main"></div>

<script id="my-prose" type="text/mustache">
<x-markdown>
# Hey there!
This is written in markdown.

    
- There are lists
- And _italics_
    

**And bold!**
</x-markdown>
</script>

x-markdown {
    font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", 
  Helvetica, Arial, "Lucida Grande", sans-serif;
}