remark-flexible-toc

This package is a unified (remark) plugin to expose the table of contents via Vfile.data or via an option reference in markdown.

unified is a project that transforms content with abstract syntax trees (ASTs) using the new parser micromark. remark adds support for markdown to unified. mdast is the Markdown Abstract Syntax Tree (AST) which is a specification for representing markdown in a syntax tree.

This plugin is a remark plugin that doesn't transform the mdast but gets info from the mdast.

When should I use this?

This plugin remark-flexible-toc is useful if you want to get the table of contents (TOC) from the markdown/MDX document. The remark-flexible-toc exposes the table of contents (TOC) in two ways:

• by adding the toc into the Vfile.data
• by mutating a reference array if provided in the options

Installation

This package is suitable for ESM only. In Node.js (version 16+), install with npm:

npm install remark-flexible-toc

or

yarn add remark-flexible-toc

Usage

Say we have the following file, example.md, which consists some headings.

# The Main Heading

## Section

### Subheading 1

### Subheading 2

And our module, example.js, looks as follows:

import { read } from "to-vfile";
import remark from "remark";
import gfm from "remark-gfm";
import remarkRehype from "remark-rehype";
import rehypeStringify from "rehype-stringify";
import remarkFlexibleToc from "remark-flexible-toc";

main();

async function main() {
  const toc = [];

  const file = await remark()
    .use(gfm)
    .use(remarkFlexibleToc, {tocRef: toc})
    .use(remarkRehype)
    .use(rehypeStringify)
    .process(await read("example.md"));

  // the first way of getting TOC via file.data
  console.log(file.data.toc);

  // the second way of getting TOC, since we provided a reference array in the options
  console.log(toc);
}

Now, running node example.js you see that the same table of contents is logged in the console:

[
  {
    depth: 2,
    href: "#section",
    numbering: [1, 1],
    parent: "root",
    value: "Section",
  },
  {
    depth: 3,
    href: "#subheading-1",
    numbering: [1, 1, 1],
    parent: "root",
    value: "Subheading 1",
  },
  {
    depth: 3,
    href: "#subheading-2",
    numbering: [1, 1, 2],
    parent: "root",
    value: "Subheading 2",
  },
]

Without remark-flexible-toc, there wouldn't be any toc key in the file.data:

Options

All options are optional.

type HeadingParent =
  | "root"
  | "blockquote"
  | "footnoteDefinition"
  | "listItem"
  | "container"
  | "mdxJsxFlowElement";

type HeadingDepth = 1 | 2 | 3 | 4 | 5 | 6;

use(remarkFlexibleToc, {
  tocName?: string; // default: "toc"
  tocRef?: TocItem[]; // default: []
  maxDepth?: HeadingDepth; // default: 6
  skipLevels?: HeadingDepth[]; // default: [1]
  skipParents?: Exclude<HeadingParent, "root">[]; // default: []
  exclude?: string | string[];
  prefix?: string;
  fallback?: (toc: TocItem[]) => undefined;
} as FlexibleTocOptions);

tocName

It is a string option in which the table of contents (TOC) is placed in the vfile.data.

By default it is toc, meaningly the TOC is reachable via vfile.data.toc.

use(remarkFlexibleToc, {
  tocName: "headings";
});

Now, the TOC is accessable via vfile.data.headings.

tocRef

It is an array of reference option for getting the table of contents (TOC), which is the second way of getting the TOC from the remark-flexible-toc.

The reference array should be an empty array, if not, it is emptied by the plugin.

If you use typescript, the array reference should be const toc: TocItem[] = [].

const toc = [];

use(remarkFlexibleToc, {
  tocRef: toc; // the `remark-flexible-toc` mutates the array of reference
});

Now, the TOC is accessable via toc.

maxDepth

It is a number option for indicating the max heading depth to include in the TOC.

By default it is 6. Meaningly, there is no restriction by default.

use(remarkFlexibleToc, {
  maxDepth: 4;
});

The maxDepth option is inclusive: when set to 4, level fourth headings are included, but fifth and sixth level headings will be skipped.

skipLevels

It is an array option to indicate the heading levels to be skipped.

By default it is [1] since the first level heading is not expected to be in the TOC.

use(remarkFlexibleToc, {
  skipLevels: [1, 2, 4, 5, 6];
});

Now, the TOC consists only the third level headings.

skipParents

By default it is an empty array []. The array may contain the parent values blockquote, footnoteDefinition, listItem, container, mdxJsxFlowElement.

use(remarkFlexibleToc, {
  skipParents: ["blockquote"];
});

Now, the headings in the <blockquote> will not be added into the TOC.

exclude

It is a string or string[] option. The plugin wraps the string(s) in new RegExp('^(' + value + ')$', 'i'), so any heading matching this expression will not be present in the TOC. The RegExp checks exact (not contain) matching and case insensitive as you see.

The option has no default value.

use(remarkFlexibleToc, {
  exclude: "The Subheading";
});

Now, the heading "The Subheading" will not be included in to the TOC, but forexample "The Subheading Something" will be included.

prefix

It is a string option to add a prefix to hrefs of the TOC items. It is useful for example when later going from markdown to HTML and sanitizing with rehype-sanitize.

The option has no default value.

use(remarkFlexibleToc, {
  prefix: "text-prefix-";
});

Now, all TOC items' hrefs will start with that prefix like #text-prefix-the-subheading.

callback

It is a callback function callback?: (toc: TocItem[]) => undefined; which takes the TOC items as an argument and returns nothing. It is usefull for logging the TOC, forexample, or modifing the TOC. It is allowed that the callback function is able to mutate the TOC items !

The option has no default value.

use(remarkFlexibleToc, {
  callback: (toc) => {
    console.log(toc);
  };
});

Now, each time when you compile the source, the TOC will be logged into the console for debugging purpose.

A Table of Content (TOC) Item

type TocItem = {
  value: string; // heading text
  href: string; // produced uniquely by "github-slugger" using the value of the heading
  depth: HeadingDepth; // 1 | 2 | 3 | 4 | 5 | 6
  numbering: number[]; // explained below
  parent: HeadingParent; // "root"| "blockquote" | "footnoteDefinition" | "listItem" | "container" | "mdxJsxFlowElement"
  data?: Record<string, unknown>; // Other remark plugins may store custom data in "node.data.hProperties" like "id" etc.
};

Note

If there is a remark plugin before the remark-flexible-toc in the plugin chain, which provides custom id for headings like remark-heading-id, that custom id takes precedence for href.

The remark-flexible-toc uses the github-slugger internally for producing unique links. Then, it is possible you to use rehype-slug (forIDs on headings) and rehype-autolink-headings (for anchors that link-to-self) because they use the same github-slugger.

As an example for the unique heading links (notice the same heading texts).

# The Main Heading

## Section

### Subheading

## Section
      
### Subheading

The github-slugger produces unique links with using a counter mechanism internally, and the TOC item's hrefs is going to be unique.

[
  {
    depth: 2,
    href: "#section",
    numbering: [1, 1],
    parent: "root",
    value: "Section",
  },
  {
    depth: 3,
    href: "#subheading",
    numbering: [1, 1, 1],
    parent: "root",
    value: "Subheading",
  },
  {
    depth: 2,
    href: "#section-1",
    numbering: [1, 2],
    parent: "root",
    value: "Section",
  },
  {
    depth: 3,
    href: "#subheading-1",
    numbering: [1, 2, 1],
    parent: "root",
    value: "Subheading",
  },
]

Numbering for Ordered Table of Contents (TOC)

The remark-flexible-toc produces always the numbering for TOC items in case you show the ordered TOC.

The numbering of a TOC item is an array of number. The numbers in the numbering corresponds the level of the headers. With that structure, you know which header is under which header.

[1, 1]
[1, 2]
[1, 2, 1]
[1, 2, 2]
[1, 3]

The first number of the numbering is related with the fist level headings. The second number of the numbering is related with the second level headings. And so on...

If yo haven't included the first level header into the TOC, you can slice the numbering with 1 so as to second level headings starts with 1 and so on..

tocItem.numbering.slice(1);

You can join the numbering as you wish. It is up to you to combine the numbering with dot, or dash.

tocItem.numbering.join(".");
tocItem.numbering.join("-");

Syntax tree

This plugin does not modify the mdast (markdown abstract syntax tree), collects data from the mdast and adds information into the vfile.data if required.

Types

This package is fully typed with TypeScript.

The plugin exports the types FlexibleTocOptions, HeadingParent, HeadingDepth, TocItem.

Compatibility

This plugin works with unified version 6+ and remark version 7+. It is compatible with mdx version 2+.

Security

Use of remark-flexible-toc does not involve rehype (hast) or user content so there are no openings for cross-site scripting (XSS) attacks.

My Plugins

I like to contribute the Unified / Remark / MDX ecosystem, so I recommend you to have a look my plugins.

My Remark Plugins

• remark-flexible-code-titles – Remark plugin to add titles or/and containers for the code blocks with customizable properties
• remark-flexible-containers – Remark plugin to add custom containers with customizable properties in markdown
• remark-ins – Remark plugin to add ins element in markdown
• remark-flexible-paragraphs – Remark plugin to add custom paragraphs with customizable properties in markdown
• remark-flexible-markers – Remark plugin to add custom mark element with customizable properties in markdown
• remark-flexible-toc – Remark plugin to expose the table of contents via vfile.data or via an option reference
• remark-mdx-remove-esm – Remark plugin to remove import and/or export statements (mdxjsEsm)

My Rehype Plugins

• rehype-pre-language – Rehype plugin to add language information as a property to pre element
• rehype-highlight-code-lines – Rehype plugin to add line numbers to code blocks and allow highlighting of desired code lines

My Recma Plugins

• recma-mdx-escape-missing-components – Recma plugin to set the default value () => null for the Components in MDX in case of missing or not provided so as not to throw an error
• recma-mdx-change-props – Recma plugin to change the props parameter into the _props in the function _createMdxContent(props) {/* */} in the compiled source in order to be able to use {props.foo} like expressions. It is useful for the next-mdx-remote or next-mdx-remote-client users in nextjs applications.

License

MIT License © ipikuka

Keywords

🟩 unified 🟩 remark 🟩 remark plugin 🟩 mdast 🟩 markdown 🟩 mdx 🟩 remark toc 🟩 remark table of contents