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https://github.com/remarkjs/react-markdown

Markdown component for React
https://github.com/remarkjs/react-markdown

commonmark gfm markdown react remark

Last synced: about 2 months ago
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Markdown component for React

Awesome Lists containing this project

README 

        



# react-markdown



[![Build][build-badge]][build]

[![Coverage][coverage-badge]][coverage]

[![Downloads][downloads-badge]][downloads]

[![Size][size-badge]][size]

[![Sponsors][sponsors-badge]][collective]

[![Backers][backers-badge]][collective]

[![Chat][chat-badge]][chat]



React component to render markdown.



## Feature highlights



* [x] **[safe][section-security] by default**

  (no `dangerouslySetInnerHTML` or XSS attacks)

* [x] **[components][section-components]**

  (pass your own component to use instead of `
` for `## hi`)

* [x] **[plugins][section-plugins]**

  (many plugins you can pick and choose from)

* [x] **[compliant][section-syntax]**

  (100% to CommonMark, 100% to GFM with a plugin)



## Contents



* [What is this?](#what-is-this)

* [When should I use this?](#when-should-i-use-this)

* [Install](#install)

* [Use](#use)

* [API](#api)

  * [`Markdown`](#markdown)

  * [`defaultUrlTransform(url)`](#defaulturltransformurl)

  * [`AllowElement`](#allowelement)

  * [`Components`](#components)

  * [`ExtraProps`](#extraprops)

  * [`Options`](#options)

  * [`UrlTransform`](#urltransform)

* [Examples](#examples)

  * [Use a plugin](#use-a-plugin)

  * [Use a plugin with options](#use-a-plugin-with-options)

  * [Use custom components (syntax highlight)](#use-custom-components-syntax-highlight)

  * [Use remark and rehype plugins (math)](#use-remark-and-rehype-plugins-math)

* [Plugins](#plugins)

* [Syntax](#syntax)

* [Types](#types)

* [Compatibility](#compatibility)

* [Architecture](#architecture)

* [Appendix A: HTML in markdown](#appendix-a-html-in-markdown)

* [Appendix B: Components](#appendix-b-components)

* [Appendix C: line endings in markdown (and JSX)](#appendix-c-line-endings-in-markdown-and-jsx)

* [Security](#security)

* [Related](#related)

* [Contribute](#contribute)

* [License](#license)



## What is this?



This package is a [React][] component that can be given a string of markdown

that it’ll safely render to React elements.

You can pass plugins to change how markdown is transformed and pass components

that will be used instead of normal HTML elements.



* to learn markdown, see this [cheatsheet and tutorial][commonmark-help]

* to try out `react-markdown`, see [our demo][demo]



## When should I use this?



There are other ways to use markdown in React out there so why use this one?

The three main reasons are that they often rely on `dangerouslySetInnerHTML`,

have bugs with how they handle markdown, or don’t let you swap elements for

components.

`react-markdown` builds a virtual DOM, so React only replaces what changed,

from a syntax tree.

That’s supported because we use [unified][], specifically [remark][] for

markdown and [rehype][] for HTML, which are popular tools to transform content

with plugins.



This package focusses on making it easy for beginners to safely use markdown in

React.

When you’re familiar with unified, you can use a modern hooks based alternative

[`react-remark`][react-remark] or [`rehype-react`][rehype-react] manually.

If you instead want to use JavaScript and JSX *inside* markdown files, use

[MDX][].



## Install



This package is [ESM only][esm].

In Node.js (version 16+), install with [npm][]:



```sh

npm install react-markdown

```



In Deno with [`esm.sh`][esmsh]:



```js

import Markdown from 'https://esm.sh/react-markdown@9'

```



In browsers with [`esm.sh`][esmsh]:



```html



  import Markdown from 'https://esm.sh/react-markdown@9?bundle'



```



## Use



A basic hello world:



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'



const markdown = '# Hi, *Pluto*!'



createRoot(document.body).render({markdown})

```



Show equivalent JSX



```jsx



  Hi, Pluto!



```



Here is an example that shows how to use a plugin ([`remark-gfm`][remark-gfm],

which adds support for footnotes, strikethrough, tables, tasklists and URLs

directly):



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import remarkGfm from 'remark-gfm'



const markdown = `Just a link: www.nasa.gov.`



createRoot(document.body).render(

  {markdown}

)

```



Show equivalent JSX



```jsx



  Just a link: www.nasa.gov.



```



## API



This package exports the following identifier:

[`defaultUrlTransform`][api-default-url-transform].

The default export is [`Markdown`][api-markdown].



### `Markdown`



Component to render markdown.



###### Parameters



* `options` ([`Options`][api-options])

  — props



###### Returns



React element (`JSX.Element`).



### `defaultUrlTransform(url)`



Make a URL safe.



###### Parameters



* `url` (`string`)

  — URL



###### Returns



Safe URL (`string`).



### `AllowElement`



Filter elements (TypeScript type).



###### Parameters



* `node` ([`Element` from `hast`][hast-element])

  — element to check

* `index` (`number | undefined`)

  — index of `element` in `parent`

* `parent` ([`Node` from `hast`][hast-node])

  — parent of `element`



###### Returns



Whether to allow `element` (`boolean`, optional).



### `Components`



Map tag names to components (TypeScript type).



###### Type



```ts

import type {Element} from 'hast'



type Components = Partial<{

  [TagName in keyof JSX.IntrinsicElements]:

    // Class component:

    | (new (props: JSX.IntrinsicElements[TagName] & ExtraProps) => JSX.ElementClass)

    // Function component:

    | ((props: JSX.IntrinsicElements[TagName] & ExtraProps) => JSX.Element | string | null | undefined)

    // Tag name:

    | keyof JSX.IntrinsicElements

}>

```



### `ExtraProps`



Extra fields we pass to components (TypeScript type).



###### Fields



* `node` ([`Element` from `hast`][hast-element], optional)

  — original node



### `Options`



Configuration (TypeScript type).



###### Fields



* `allowElement` ([`AllowElement`][api-allow-element], optional)

  — filter elements;

  `allowedElements` / `disallowedElements` is used first

* `allowedElements` (`Array`, default: all tag names)

  — tag names to allow;

  cannot combine w/ `disallowedElements`

* `children` (`string`, optional)

  — markdown

* `className` (`string`, optional)

  — wrap in a `div` with this class name

* `components` ([`Components`][api-components], optional)

  — map tag names to components

* `disallowedElements` (`Array`, default: `[]`)

  — tag names to disallow;

  cannot combine w/ `allowedElements`

* `rehypePlugins` (`Array`, optional)

  — list of [rehype plugins][rehype-plugins] to use

* `remarkPlugins` (`Array`, optional)

  — list of [remark plugins][remark-plugins] to use

* `remarkRehypeOptions` ([`Options` from

  `remark-rehype`][remark-rehype-options], optional)

  — options to pass through to `remark-rehype`

* `skipHtml` (`boolean`, default: `false`)

  — ignore HTML in markdown completely

* `unwrapDisallowed` (`boolean`, default: `false`)

  — extract (unwrap) what’s in disallowed elements;

  normally when say `strong` is not allowed, it and it’s children are dropped,

  with `unwrapDisallowed` the element itself is replaced by its children

* `urlTransform` ([`UrlTransform`][api-url-transform], default:

  [`defaultUrlTransform`][api-default-url-transform])

  — change URLs



### `UrlTransform`



Transform URLs (TypeScript type).



###### Parameters



* `url` (`string`)

  — URL

* `key` (`string`, example: `'href'`)

  — property name

* `node` ([`Element` from `hast`][hast-element])

  — element to check



###### Returns



Transformed URL (`string`, optional).



## Examples



### Use a plugin



This example shows how to use a remark plugin.

In this case, [`remark-gfm`][remark-gfm], which adds support for strikethrough,

tables, tasklists and URLs directly:



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import remarkGfm from 'remark-gfm'



const markdown = `A paragraph with *emphasis* and **strong importance**.



> A block quote with ~strikethrough~ and a URL: https://reactjs.org.



* Lists

* [ ] todo

* [x] done



A table:



| a | b |

| - | - |

`



createRoot(document.body).render(

  {markdown}

)

```



Show equivalent JSX



```jsx

<>

  


    A paragraph with emphasis and strong importance.

  


  


    


      A block quote with strikethrough and a URL:{' '}

      https://reactjs.org.

    


  


  
    

        
  • Lists
    • 

        
  • 

           todo

        
    • 

        
  • 

           done

        
    • 

      


  
A table:


  

    

      

        a

        b

      

    

  

>

```



### Use a plugin with options



This example shows how to use a plugin and give it options.

To do that, use an array with the plugin at the first place, and the options

second.

[`remark-gfm`][remark-gfm] has an option to allow only double tildes for

strikethrough:



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import remarkGfm from 'remark-gfm'



const markdown = 'This ~is not~ strikethrough, but ~~this is~~!'



createRoot(document.body).render(

  

    {markdown}

  

)

```



Show equivalent JSX



```jsx



  This ~is not~ strikethrough, but this is!



```



### Use custom components (syntax highlight)



This example shows how you can overwrite the normal handling of an element by

passing a component.

In this case, we apply syntax highlighting with the seriously super amazing

[`react-syntax-highlighter`][react-syntax-highlighter] by

[**@conorhastings**][conor]:



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import {Prism as SyntaxHighlighter} from 'react-syntax-highlighter'

import {dark} from 'react-syntax-highlighter/dist/esm/styles/prism'



// Did you know you can use tildes instead of backticks for code in markdown? ✨

const markdown = `Here is some JavaScript code:



~~~js

console.log('It works!')

~~~

`



createRoot(document.body).render(

  

        ) : (

          

            {children}

          

        )

      }

    }}

  />

)

```



Show equivalent JSX



```jsx

<>

  
Here is some JavaScript code:


  

    

  


>

```



### Use remark and rehype plugins (math)



This example shows how a syntax extension (through [`remark-math`][remark-math])

is used to support math in markdown, and a transform plugin

([`rehype-katex`][rehype-katex]) to render that math.



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import rehypeKatex from 'rehype-katex'

import remarkMath from 'remark-math'

import 'katex/dist/katex.min.css' // `rehype-katex` does not import the CSS for you



const markdown = `The lift coefficient ($C_L$) is a dimensionless coefficient.`



createRoot(document.body).render(

  

    {markdown}

  

)

```



Show equivalent JSX



```jsx



  The lift coefficient (

  

    

      {/* … */}

    

    

      {/* … */}

    

  

  ) is a dimensionless coefficient.



```



## Plugins



We use [unified][], specifically [remark][] for markdown and [rehype][] for

HTML, which are tools to transform content with plugins.

Here are three good ways to find plugins:



* [`awesome-remark`][awesome-remark] and [`awesome-rehype`][awesome-rehype]

  — selection of the most awesome projects

* [List of remark plugins][remark-plugins] and

  [list of rehype plugins][rehype-plugins]

  — list of all plugins

* [`remark-plugin`][remark-plugin] and [`rehype-plugin`][rehype-plugin] topics

  — any tagged repo on GitHub



## Syntax



`react-markdown` follows CommonMark, which standardizes the differences between

markdown implementations, by default.

Some syntax extensions are supported through plugins.



We use [`micromark`][micromark] under the hood for our parsing.

See its documentation for more information on markdown, CommonMark, and

extensions.



## Types



This package is fully typed with [TypeScript][].

It exports the additional types

[`AllowElement`][api-allow-element],

[`ExtraProps`][api-extra-props],

[`Components`][api-components],

[`Options`][api-options], and

[`UrlTransform`][api-url-transform].



## Compatibility



Projects maintained by the unified collective are compatible with maintained

versions of Node.js.



When we cut a new major release, we drop support for unmaintained versions of

Node.

This means we try to keep the current release line, `react-markdown@^9`,

compatible with Node.js 16.



They work in all modern browsers (essentially: everything not IE 11).

You can use a bundler (such as esbuild, webpack, or Rollup) to use this package

in your project, and use its options (or plugins) to add support for legacy

browsers.



## Architecture



                                                           react-markdown

         +----------------------------------------------------------------------------------------------------------------+

         |                                                                                                                |

         |  +----------+        +----------------+        +---------------+       +----------------+       +------------+ |

         |  |          |        |                |        |               |       |                |       |            | |

markdown-+->+  remark  +-mdast->+ remark plugins +-mdast->+ remark-rehype +-hast->+ rehype plugins +-hast->+ components +-+->react elements

         |  |          |        |                |        |               |       |                |       |            | |

         |  +----------+        +----------------+        +---------------+       +----------------+       +------------+ |

         |                                                                                                                |

         +----------------------------------------------------------------------------------------------------------------+




To understand what this project does, it’s important to first understand what

unified does: please read through the [`unifiedjs/unified`][unified] readme (the

part until you hit the API section is required reading).



`react-markdown` is a unified pipeline — wrapped so that most folks don’t need

to directly interact with unified.

The processor goes through these steps:



* parse markdown to mdast (markdown syntax tree)

* transform through remark (markdown ecosystem)

* transform mdast to hast (HTML syntax tree)

* transform through rehype (HTML ecosystem)

* render hast to React with components



## Appendix A: HTML in markdown



`react-markdown` typically escapes HTML (or ignores it, with `skipHtml`)

because it is dangerous and defeats the purpose of this library.



However, if you are in a trusted environment (you trust the markdown), and

can spare the bundle size (±60kb minzipped), then you can use

[`rehype-raw`][rehype-raw]:



```jsx

import React from 'react'

import {createRoot} from 'react-dom/client'

import Markdown from 'react-markdown'

import rehypeRaw from 'rehype-raw'



const markdown = `



Some *emphasis* and strong!



`



createRoot(document.body).render(

  {markdown}

)

```



Show equivalent JSX



```jsx



  


    Some emphasis and strong!

  




```



**Note**: HTML in markdown is still bound by how [HTML works in

CommonMark][commonmark-html].

Make sure to use blank lines around block-level HTML that again contains

markdown!



## Appendix B: Components



You can also change the things that come from markdown:



```jsx



    }

  }}

/>

```



The keys in components are HTML equivalents for the things you write with

markdown (such as `h1` for `# heading`).

Normally, in markdown, those are: `a`, `blockquote`, `br`, `code`, `em`, `h1`,

`h2`, `h3`, `h4`, `h5`, `h6`, `hr`, `img`, `li`, `ol`, `p`, `pre`, `strong`, and

`ul`.

With [`remark-gfm`][remark-gfm], you can also use `del`, `input`, `table`,

`tbody`, `td`, `th`, `thead`, and `tr`.

Other remark or rehype plugins that add support for new constructs will also

work with `react-markdown`.



The props that are passed are what you probably would expect: an `a` (link) will

get `href` (and `title`) props, and `img` (image) an `src`, `alt` and `title`,

etc.



Every component will receive a `node`.

This is the original [`Element` from `hast`][hast-element] element being turned

into a React element.



## Appendix C: line endings in markdown (and JSX)



You might have trouble with how line endings work in markdown and JSX.

We recommend the following, which solves all line ending problems:



```jsx

// If you write actual markdown in your code, put your markdown in a variable;

// **do not indent markdown**:

const markdown = `

# This is perfect!

`



// Pass the value as an expresion as an only child:

const result = {markdown}

```



👆 That works.

Read on for what doesn’t and why that is.



You might try to write markdown directly in your JSX and find that it **does

not** work:



```jsx



  # Hi



  This is **not** a paragraph.



```



The is because in JSX the whitespace (including line endings) is collapsed to

a single space.

So the above example is equivalent to:



```jsx

 # Hi This is **not** a paragraph. 

```



Instead, to pass markdown to `Markdown`, you can use an expression:

with a template literal:



```jsx

{`

# Hi



This is a paragraph.

`}

```



Template literals have another potential problem, because they keep whitespace

(including indentation) inside them.

That means that the following **does not** turn into a heading:



```jsx

{`

    # This is **not** a heading, it’s an indented code block

`}

```



## Security



Use of `react-markdown` is secure by default.

Overwriting `urlTransform` to something insecure will open you up to XSS

vectors.

Furthermore, the `remarkPlugins`, `rehypePlugins`, and `components` you use may

be insecure.



To make sure the content is completely safe, even after what plugins do,

use [`rehype-sanitize`][rehype-sanitize].

It lets you define your own schema of what is and isn’t allowed.



## Related



* [`MDX`][mdx]

  — JSX *in* markdown

* [`remark-gfm`][remark-gfm]

  — add support for GitHub flavored markdown support

* [`react-remark`][react-remark]

  — hook based alternative

* [`rehype-react`][rehype-react]

  — turn HTML into React elements



## Contribute



See [`contributing.md`][contributing] in [`remarkjs/.github`][health] for ways

to get started.

See [`support.md`][support] for ways to get help.



This project has a [code of conduct][coc].

By interacting with this repository, organization, or community you agree to

abide by its terms.



## License



[MIT][license] © [Espen Hovlandsdal][author]



[build-badge]: https://github.com/remarkjs/react-markdown/workflows/main/badge.svg



[build]: https://github.com/remarkjs/react-markdown/actions



[coverage-badge]: https://img.shields.io/codecov/c/github/remarkjs/react-markdown.svg



[coverage]: https://codecov.io/github/remarkjs/react-markdown



[downloads-badge]: https://img.shields.io/npm/dm/react-markdown.svg



[downloads]: https://www.npmjs.com/package/react-markdown



[size-badge]: https://img.shields.io/bundlejs/size/react-markdown



[size]: https://bundlejs.com/?q=react-markdown



[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg



[backers-badge]: https://opencollective.com/unified/backers/badge.svg



[collective]: https://opencollective.com/unified



[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg



[chat]: https://github.com/remarkjs/remark/discussions



[npm]: https://docs.npmjs.com/cli/install



[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c



[esmsh]: https://esm.sh



[health]: https://github.com/remarkjs/.github



[coc]: https://github.com/remarkjs/.github/blob/main/code-of-conduct.md



[contributing]: https://github.com/remarkjs/.github/blob/main/contributing.md



[support]: https://github.com/remarkjs/.github/blob/main/support.md



[license]: license



[author]: https://espen.codes/



[awesome-remark]: https://github.com/remarkjs/awesome-remark



[awesome-rehype]: https://github.com/rehypejs/awesome-rehype



[commonmark-help]: https://commonmark.org/help/



[commonmark-html]: https://spec.commonmark.org/0.30/#html-blocks



[hast-element]: https://github.com/syntax-tree/hast#element



[hast-node]: https://github.com/syntax-tree/hast#nodes



[mdx]: https://github.com/mdx-js/mdx/



[micromark]: https://github.com/micromark/micromark



[react]: http://reactjs.org



[react-remark]: https://github.com/remarkjs/react-remark



[react-syntax-highlighter]: https://github.com/react-syntax-highlighter/react-syntax-highlighter



[rehype]: https://github.com/rehypejs/rehype



[rehype-katex]: https://github.com/remarkjs/remark-math/tree/main/packages/rehype-katex



[rehype-plugin]: https://github.com/topics/rehype-plugin



[rehype-plugins]: https://github.com/rehypejs/rehype/blob/main/doc/plugins.md#list-of-plugins



[rehype-react]: https://github.com/rehypejs/rehype-react



[rehype-raw]: https://github.com/rehypejs/rehype-raw



[rehype-sanitize]: https://github.com/rehypejs/rehype-sanitize



[remark]: https://github.com/remarkjs/remark



[remark-gfm]: https://github.com/remarkjs/remark-gfm



[remark-math]: https://github.com/remarkjs/remark-math



[remark-plugin]: https://github.com/topics/remark-plugin



[remark-plugins]: https://github.com/remarkjs/remark/blob/main/doc/plugins.md#list-of-plugins



[remark-rehype-options]: https://github.com/remarkjs/remark-rehype#options



[unified]: https://github.com/unifiedjs/unified



[typescript]: https://www.typescriptlang.org



[conor]: https://github.com/conorhastings



[demo]: https://remarkjs.github.io/react-markdown/



[section-components]: #appendix-b-components



[section-plugins]: #plugins



[section-security]: #security



[section-syntax]: #syntax



[api-allow-element]: #allowelement



[api-components]: #components



[api-default-url-transform]: #defaulturltransformurl



[api-extra-props]: #extraprops



[api-markdown]: #markdown



[api-options]: #options



[api-url-transform]: #urltransform