using nunjucks to parse yaml front matter item without knowing its structure

[btrem]

I have a yaml front matter item that might be a list:

foo:
  - bar1
  - bar2
  - bar3

or it might be a dictionary:

foo:
  bar1: baz
  bar2: 2
  bar3: 3 baz

Is there a way to parse foo in a nunjucks template? For the list, I need {% for item in foo %}; for the dictionary, I need {% for item, value in foo %}. But I can't figure if I can determine the nature of foo in nunjucks in order to choose the right for loop.

[pdehaan]

I couldn't easily figure out how to call Array.isArray(), but I was able to do it with a custom filter and a slightly verbose {% if %}...{% else %}...{% endif %} block:

eleventyConfig.addFilter("isArray", Array.isArray);

USAGE

---
title: Bleep bloop
foo2:
  - bar1
  - bar2
  - bar3

foo:
  bar1: baz
  bar2: 2
  bar3: 3 baz
---

{% if foo | isArray %}
  {% for item in foo %}
    - {{ item }}
  {% endfor %}
{% else %}
  {% for item, value in foo %}
    - {{ item }}; {{ value }}
  {% endfor %}
{% endif %}