Okay, I’ve added h to the pluginApi object as long as you request plugin api v0.3:
<script type="text/discourse-plugin" version="0.3">
console.log(api.h('b', ['hello', 'world']));
</script>
That should work for you!
https://github.com/discourse/discourse/commit/b10b6c673d5f4936d0ee107e16531df106fae75e