test-body-template.html

<template id="test-template">
    <div>
        <span>test-template</span>
        <span v-html="content" />
    </div>
</template>

<script>
    kiwi.plugin('test-body-template', function (kiwi, log) {
        const testTemplate = {
            template: '#test-template',
            data() {
                return {
                    content: '',
                    show: true,
                };
            },
            mounted() {
                console.log('test-template mounted');
            },
        };

        const testTemplateComponent = kiwi.Vue.extend(testTemplate);

        kiwi.state.$on('message.poststyle', function (event) {
            if (!event.message || event.message.type !== 'privmsg') {
                return;
            }

            const content = event.message.html;

            if (!content) {
                console.log('no content');
                return;
            }

            console.log('adding template', content, event);
            event.message.bodyTemplate = new testTemplateComponent({
                data: {
                    content: content,
                },
            });
            event.message.bodyTemplate.$mount();
            event.message.embed.payload = null;
            event.message.html = '';
        });
    });
</script>