react-markdown
React component to render markdown.
Feature highlights
- [x] safe by default
(no
dangerouslySetInnerHTML or XSS attacks)
- [x] components
(pass your own component to use instead of
<h2> for ## hi)
- [x] plugins
(many plugins you can pick and choose from)
- [x] compliant
(100% to CommonMark, 100% to GFM with a plugin)
Contents
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.
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 or rehype-react
manually.
If you instead want to use JavaScript and JSX inside markdown files, use
MDX.
Install
This package is ESM only.
In Node.js (version 16+), install with npm:
npm install react-markdown
In Deno with esm.sh:
import Markdown from 'https://esm.sh/react-markdown@10'
In browsers with esm.sh:
<script type="module">
import Markdown from 'https://esm.sh/react-markdown@10?bundle'
</script>
Use
A basic hello world:
import React from 'react'
import {createRoot} from 'react-dom/client'
import Markdown from 'react-markdown'
const markdown = '# Hi, *Pluto*!'
createRoot(document.body).render(<Markdown>{markdown}</Markdown>)
Show equivalent JSX
<h1>
Hi, <em>Pluto</em>!
</h1>
Here is an example that shows how to use a plugin
(remark-gfm,
which adds support for footnotes, strikethrough, tables, tasklists and
URLs directly):
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 remarkPlugins={[remarkGfm]}>{markdown}</Markdown>
)
Show equivalent JSX
<p>
Just a link: <a href="http://www.nasa.gov">www.nasa.gov</a>.
</p>
API
This package exports the identifiers
MarkdownAsync,
MarkdownHooks,
and
defaultUrlTransform.
The default export is Markdown.
Markdown
Component to render markdown.
This is a synchronous component.
When using async plugins,
see MarkdownAsync or
MarkdownHooks.
Parameters
Returns
React element (JSX.Element).
MarkdownAsync
Component to render markdown with support for async plugins
through async/await.
Components returning promises are supported on the server.
For async support on the client,
see MarkdownHooks.
Parameters
Returns
Promise to a React element (Promise<JSX.Element>).
MarkdownHooks
Component to render markdown with support for async plugins through hooks.
This uses useEffect and useState hooks.
Hooks run on the client and do not immediately render something.
For async support on the server,
see MarkdownAsync.
Parameters
Returns
React element (JSX.Element).
defaultUrlTransform(url)
Make a URL safe.
Parameters
Returns
Safe URL (string).
AllowElement
Filter elements (TypeScript type).
Parameters
Returns
Whether to allow element (boolean, optional).
Components
Map tag names to components (TypeScript type).
Type
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
Options
Configuration (TypeScript type).
Fields
allowElement (AllowElement, optional)
— filter elements;
allowedElements / disallowedElements is used firstallowedElements (Array<string>, default: all tag names)
— tag names to allow;
cannot combine w/ disallowedElementschildren (string, optional)
— markdowncomponents (Components, optional)
— map tag names to componentsdisallowedElements (Array<string>, default: [])
— tag names to disallow;
cannot combine w/ allowedElementsrehypePlugins (Array<Plugin>, optional)
— list of rehype plugins to useremarkPlugins (Array<Plugin>, optional)
— list of remark plugins to useremarkRehypeOptions
(Options from remark-rehype,
optional)
— options to pass through to remark-rehypeskipHtml (boolean, default: false)
— ignore HTML in markdown completelyunwrapDisallowed (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 childrenurlTransform (UrlTransform, default:
defaultUrlTransform)
— change URLs
UrlTransform
Transform URLs (TypeScript type).
Parameters
url (string)
— URLkey (string, example: 'href')
— property namenode (Element from hast)
— 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,
which adds support for strikethrough, tables, tasklists and URLs directly:
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 remarkPlugins={[remarkGfm]}>{markdown}</Markdown>
)
Show equivalent JSX
<>
<p>
A paragraph with <em>emphasis</em> and <strong>strong importance</strong>.
</p>
<blockquote>
<p>
A block quote with <del>strikethrough</del> and a URL:{' '}
<a href="https://reactjs.org">https://reactjs.org</a>.
</p>
</blockquote>
<ul className="contains-task-list">
<li>Lists</li>
<li className="task-list-item">
<input type="checkbox" disabled /> todo
</li>
<li className="task-list-item">
<input type="checkbox" disabled checked /> done
</li>
</ul>
<p>A table:</p>
<table>
<thead>
<tr>
<th>a</th>
<th>b</th>
</tr>
</thead>
</table>
</>
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 has an option to allow only double tildes for
strikethrough:
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 remarkPlugins={[[remarkGfm, {singleTilde: false}]]}>
{markdown}
</Markdown>
)
Show equivalent JSX
<p>
This ~is not~ strikethrough, but <del>this is</del>!
</p>
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 by
@conorhastings:
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(
<Markdown
children={markdown}
components={{
code(props) {
const {children, className, node, ...rest} = props
const match = /language-(\w+)/.exec(className || '')
return match ? (
<SyntaxHighlighter
{...rest}
PreTag="div"
children={String(children).replace(/\n$/, '')}
language={match[1]}
style={dark}
/>
) : (
<code {...rest} className={className}>
{children}
</code>
)
}
}}
/>
)
Show equivalent JSX
<>
<p>Here is some JavaScript code:</p>
<pre>
<SyntaxHighlighter language="js" style={dark} PreTag="div" children="console.log('It works!')" />
</pre>
</>
Use remark and rehype plugins (math)
This example shows how a syntax extension
(through remark-math)
is used to support math in markdown, and a transform plugin
(rehype-katex) to render that math.
import React from 'react'
import {createRoot} from 'react-dom/client'
import Markdown from 'react-markdown'
import rehypeKatex from 'rehype-katex'
import remarkMath from 'remark-math'
import 'katex/dist/katex.min.css' // `rehype-katex` does not import the CSS for you
const markdown = `The lift coefficient ($C_L$) is a dimensionless coefficient.`
createRoot(document.body).render(
<Markdown remarkPlugins={[remarkMath]} rehypePlugins={[rehypeKatex]}>
{markdown}
</Markdown>
)
Show equivalent JSX
<p>
The lift coefficient (
<span className="katex">
<span className="katex-mathml">
<math xmlns="http://www.w3.org/1998/Math/MathML">{/* … */}</math>
</span>
<span className="katex-html" aria-hidden="true">
{/* … */}
</span>
</span>
) is a dimensionless coefficient.
</p>
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:
Syntax
react-markdown follows CommonMark, which standardizes the differences between
markdown implementations, by default.
Some syntax extensions are supported through plugins.
We use 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,
ExtraProps,
Components,
Options, and
UrlTransform.
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@10,
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
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:
import React from 'react'
import {createRoot} from 'react-dom/client'
import Markdown from 'react-markdown'
import rehypeRaw from 'rehype-raw'
const markdown = `<div class="note">
Some *emphasis* and <strong>strong</strong>!
</div>`
createRoot(document.body).render(
<Markdown rehypePlugins={[rehypeRaw]}>{markdown}</Markdown>
)
Show equivalent JSX
<div className="note">
<p>
Some <em>emphasis</em> and <strong>strong</strong>!
</p>
</div>
Note: HTML in markdown is still bound by how HTML works in
CommonMark.
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:
<Markdown
components={{
// Map `h1` (`# heading`) to use `h2`s.
h1: 'h2',
// Rewrite `em`s (`*like so*`) to `i` with a red foreground color.
em(props) {
const {node, ...rest} = props
return <i style={{color: 'red'}} {...rest} />
}
}}
/>
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,
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 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:
// 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 expression as an only child:
const result = <Markdown>{markdown}</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:
<Markdown>
# Hi
This is **not** a paragraph.
</Markdown>
The is because in JSX the whitespace (including line endings) is collapsed to
a single space.
So the above example is equivalent to:
<Markdown> # Hi This is **not** a paragraph. </Markdown>
Instead, to pass markdown to Markdown, you can use an expression:
with a template literal:
<Markdown>{`
# Hi
This is a paragraph.
`}</Markdown>
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:
<Markdown>{`
# This is **not** a heading, it’s an indented code block
`}</Markdown>
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.
It lets you define your own schema of what is and isn’t allowed.
Related
Contribute
See contributing.md in remarkjs/.github
for ways to get started.
See support.md for ways to get help.
This project has a code of conduct.
By interacting with this repository, organization, or community you agree to
abide by its terms.
License
MIT © Espen Hovlandsdal
