How to use include when async option is passed?

I am storing email templates in files and I have header and footer file. I am trying to use async for renderFile with this template:

<%- include('header'); -%>
<h1>
  Title
</h1>
<p>
  My page
</p>
<%- include('footer'); -%>

const options = { async : true }; the includes are replaced with [object object]. how can i use include and async together?

[drewmoore]

This works for my setup:

<%- await include('header'); %>

[mde]

Ultimately we want to make all the I/O async, so opting into async rendering with the top-level async flag should be enough to make the entire tree async. You shouldn’t have to opt in to includes being async on top of that.