Calling mdast-util-to-markdown's `toMarkdown()` with table elements throw error `Cannot handle unknown node table`

[trophygeek]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected package

mdast-util-to-markdown: "^2.1.2"

Steps to reproduce

1. Pass html that includes a <table> element to toMarkdown()

function htmlToMarkdown(htmlString: string) {
  try {
    const hast = fromHtml(htmlString, {fragment: true});
    const mdast = toMdast(hast);
    return toMarkdown(mdast);  // <-- this line throws error
  } catch (error) {
    console.error('Error converting HTML to Markdown:', error);
    return `Error: ${error instanceof Error ? error.message : String(error)}`;
  }
}

Dependencies:

  "dependencies": {
    "hast-util-from-html": "^2.0.3",
    "hast-util-to-mdast": "^10.1.2",
    "mdast-util-to-markdown": "^2.1.2"
  },

Result: toMarkdown() throws the error:

Cannot handle unknown node table

The README.md has a "List of extensions" sections that seems to indicate that tables should work.

 [syntax-tree/mdast-util-gfm-table](https://github.com/syntax-tree/mdast-util-gfm-table) — GFM tables

But I don't see any table element included in the list of handlers in the code:

mdast-util-to-markdown/lib/handle/index.js

Line 24 in d0b9be9

export const handle = {

Actual behavior

toMarkdown() throws the error "Cannot handle unknown node table".

Expected behavior

Ideally, tables would be handled but at least update the README to remove it from the list of handlers.

Runtime

Node:22.13.1 Chrome:133.0.6943.54

Package manager

yarn:1.22.22

Operating system

MacOS: Sonoma 14.7.3

Build and bundle tools

Vite

[ChristianMurphy]

@trophygeek Welcome

The README.md has a "List of extensions" sections that seems to indicate that tables should work.

Extensions are optional, and not enabled by default.
Install the table extension and include it in the extensions option for the serializer https://github.com/syntax-tree/mdast-util-to-markdown?tab=readme-ov-file#optionsextensions

[wooorm]

This is documented in the readme of hast-util-to-mdast, in the Syntax and following Syntax tree sections! :)

[trophygeek]

Thanks, I must have missed it. I did read through the documentation and the code, so it's my fault for not realizing.

I think I was surprised it that it threw the error instead of just downgrading gracefully? By downgrading, I mean something like outputting the tables as plain text versus markdown tables.

toMarkdown() also did a great job with other serializers like code blocks and lists without requiring any extensions. Guess I was a bit surprised when passing in a <table> caused it to "crash". For example, strike-through text isn't supported, but doesn't throw errors and serializes as plain text.

I'm torn about the best behavior. Without the exception, I may not have realized that tables were not being handled. It was just that finding these at runtime can be jarring. I'm left wondering if there's some other html elements that I missed in my testing could cause the function to fail once it's in production?

But thanks for working on this project, it really is great!

[wooorm]

Code blocks and lists and most other things are in CommonMark, so they do not need extensions.

Are you sure strikethrough doesn’t error?! I’m quite sure that it does.

[trophygeek]

Are you sure strikethrough doesn’t error?! I’m quite sure that it does.

I tested this input "<del>like this</del>" and it works BUT I just re-tested with "Strikethrough looks <del>like this</del>" does throw an error, so you are right (of course). 🤦

I'm currently using this snippet:

    const hast = fromHtml(htmlString, {fragment: true});
    const mdast = toMdast(hast);
    return toMarkdown(mdast, {extensions: [
        gfmToMarkdown(),
      ]});

and it seems to handle most of all different types html elements without throwing errors (so far).

[wooorm]

Strikethrough is GFM and tables are GFM. This is also mentioned in the readmes I linked: “This project creates markdown according to GFM, which is a standard that’s based on CommonMark”. So yes. Your example code supports GFM. There will be no errors.