Gray-matter options?

• mdx-bundler version: 5.1.2
• node version: 14.17.3
• npm version: 6.14.13

Relevant code or config

---
title: Test Post
published: 2021-02-13
description: Shows how a post is published via MDX
---

# Test Post

This is a test post

What you did: I’m using mdx-bundler to build a nextjs static site. My frontmatter contains some date-looking things. I pass the frontmatter returned by bundleMDX as props for my component.

What happened: Since its a static site, Nextjs tries to serialize the props as part of the component and fails because it isn’t JSON serializable:

Error: Error serializing `.frontmatter.published` returned from `getStaticProps` in "/posts/[slug]".
Reason: `object` ("[object Date]") cannot be serialized as JSON. Please only return JSON serializable data types.

Problem description: There’s no way to configure the default gray-matter engine behavior.

Suggested solution: I guess the most obvious thing is to provide the ability to pass options to gray-matter.

[barrymay]

FYI - since I ran into the same issue and am a little new to gray-matter/MDX processing, after jumping thru the google-sphere to get answers I felt dropping an example usage of graymatterOptions that solves the original question would be helpful to others:

This returns published as a string, not a date, which is typical for most JSON-parsed results anyway.

import yaml from "js-yaml";

// ---- 
  await bundleMDX(source, {
    grayMatterOptions: (options) => {
      // set other gray-matter options, like excerpt
      options.engines = {
        yaml: (s) => yaml.load(s, { schema: yaml.JSON_SCHEMA }) as object,
      };
      return options;
    },
  } 
// ---- 

If you’re using matter elsewhere, use the same thing (hence the whole point of grayMatterOptions):

import yaml from "js-yaml";

// ---- 
      const { data } = matter(source, {
        engines: {
          yaml: (s) => yaml.load(s, { schema: yaml.JSON_SCHEMA }) as object,
        },
      });
// --- 

Thanks to @Arcath and @jpaas for the solution and original question 😃

[josephbales]

@barrymay You are a legend. Thanks for this tidbit! Got me going again!