React Markdown TOC Proof-of-Concept

react-markdown-toc.tsx

/*
This is based on an idea for building a table of contents on top of
React Markdown using a custom renderer. The original conversation is at

https://github.com/remarkjs/react-markdown/issues/48
*/

import React from "react";

import ReactMarkdown from "react-markdown";
import { Row, Col, Container } from "react-bootstrap";

import { HeadingProps } from "react-markdown/lib/ast-to-react";

const markdown: string = require("~static/docs/markdown.md");

export default function Documentation() {
    const toc: {
        level: number,
        id: string,
        title: string,
    }[] = [];

    // Magic.
    const addToTOC = ({children, ...props}: React.PropsWithChildren<HeadingProps>) => {
        const level = Number(props.node.tagName.match(/h(\d)/)?.slice(1));
        if (level && children && typeof children[0] === "string") {
            const id = children[0].toLowerCase().replace(/[^a-z0-9]+/g, "-");
            toc.push({
                level,
                id,
                title: children[0],
            });
            return React.createElement(
                props.node.tagName, {id}, children
            )
        } else {
            return React.createElement(props.node.tagName, props, children);
        }
    };

    function TOC() {
        return (
            <ul className="table-of-contents">
                {toc.map(({level, id, title}) => (
                    <li key={id} className={`toc-entry-level-${level}`}>
                        <a href={`#${id}`}>{title}</a>
                    </li>
                ))}
            </ul>
        );
    }

    return (
        <Container>
            <Row>
                <Col md="9" className="wall-of-text">
                    <ReactMarkdown
                        components={{
                            h2: addToTOC,
                            h3: addToTOC,
                            h4: addToTOC,
                            h5: addToTOC,
                            h6: addToTOC,
                        }}
                    >
                        {markdown}
                    </ReactMarkdown>
                </Col>
                <Col md="3">
                    {/* More magic. */}
                    <TOC />
                </Col>
            </Row>
        </Container>
    );
}

@trainoasis Have you been able to fix this issue "all headings repeated twice"?

Nice!, thank you