Using include as a function results in "include function does not exist and is not defined in the context" error

[paulgoodfield]

There are certain times where I want to return the output of a rendered template as a string, which I can then set as the value of a variable.

E.g. Rather than have {% include "path/to/partial" with {foo: 'bar'} only %} I would want to have {% set myVar = include("path/to/partial", {foo: "bar"}, false) %}

Although I've used this without problems on other websites using Twig (e.g. Craft CMS), it doesn't look like this functionality is available with this package? When I try to use include as a function, I get the following error in my terminal:

TwigException: include function does not exist and is not defined in the context

I'm assuming there is a way around this by adding Twig.exports.extendFunction('include', ...) to the grunt config for the task, but I'm having trouble working this out. Any help would be appreciated.