@bacons/mdx
v0.4.0
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Universal MDX renderer for React Native
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@bacons/mdx
Build-time MDX for Expo apps and websites.
Add the package to your npm dependencies
yarn add @bacons/mdx
Setup
Add support for importing md
and mdx
files in your metro.config.js
file.
metro.config.js
const { getDefaultConfig } = require("expo/metro-config");
const config = getDefaultConfig(__dirname);
config.resolver.sourceExts.push("md", "mdx");
config.transformer.babelTransformerPath = require.resolve("./transformer.js");
module.exports = config;
Create a custom metro transformer. This is used to transform MDX files into JS + React Native before transpiling with Babel.
./transformer.js
const upstreamTransformer = require("@expo/metro-config/babel-transformer");
const MdxTransformer = require("@bacons/mdx/metro-transformer");
module.exports.transform = async (props) => {
// Then pass it to the upstream transformer.
return upstreamTransformer.transform(
// Transpile MDX first.
await MdxTransformer.transform(props)
);
};
Usage
Create a markdown file:
./demo.mdx
import { CustomComponent } from './my-custom-component';
# Hello World
I **am** a _markdown_ file!
<CustomComponent />
This file can be imported and treated as a React component:
./App.js
import Demo from "./demo.mdx";
export default function App() {
return <Demo />;
}
Custom components
By default, this package uses an incomplete set of universal React Native components for DOM elements. You may wish to improve the components, add more, or swap them out for your own.
import { Text } from "react-native";
import { MDXComponents } from "@bacons/mdx";
export default function App() {
return (
<Demo
components={{
h1: (props) => <h1 {...props} />,
// Add custom components which can be used as JSX elements.
RedText: (props) => <Text {...props} style={{ color: "red" }} />,
// This can be used as `<RedText />` without the need to import it.
}}
/>
);
}
Now inside of your markdown file, you can use the custom components:
# Hello World
<RedText />
You can set the components for all children using the MDXComponents
React context component.
import { Text } from "react-native";
import { MDXComponents } from "@bacons/mdx";
export default function App() {
// Pass any HTML element as a key to the MDXComponents component.
return (
<MDXComponents
components={{
h1: (props) => <Text {...props} />,
// Add custom components which can be used as JSX elements.
RedText: (props) => <Text {...props} style={{ color: "red" }} />,
// This can be used as `<RedText />` without the need to import it.
}}
>
<Demo />
</MDXComponents>
);
}
Be sure to pass the
style
prop down to the component you're using, this is how the styles are cascaded.
Custom styles
This package works similarly to most docs sites. You create high-level styles for the entire site. This can be cascaded down to reduce the scope of a style.
import { MDXStyles } from "@bacons/mdx";
export default function App() {
// Pass any HTML element as a key to the MDXStyles component.
return (
<MDXStyles
h1={{
fontSize: 32,
fontWeight: "bold",
color: "red",
}}
>
<Demo />
</MDXStyles>
);
}
The <MDXStyles>
components can be stacked in different levels, think of these like CSS classes.
Typescript
You can add support for importing .mdx
files in your tsconfig.json
file.
tsconfig.json
{
"compilerOptions": {
"typeRoots": ["./global.d.ts"]
},
"extends": "expo/tsconfig.base"
}
Now create a file that declares the module.
./global.d.ts
declare module "*.mdx" {
import React from "react";
import { CustomComponentsProp } from "@bacons/mdx";
const Component: React.FC<{
components?: CustomComponentsProp;
}>;
export default Component;
}
Experimental native errors
Optional native-only step, not required for MDX to work.
React Native has suboptimal error messages for when you use React DOM components on native or render strings outside of <Text />
elements. This can make migration and code sharing very painful. This package has an experimental dev-only feature to print out optimized errors when you render react-dom built-in's such as div, p, h1, etc. on native.
Simply add the following to your babel.config.js
, and clear the transform cache npx expo start --clear
:
module.exports = function (api) {
api.cache(true);
return {
presets: [["babel-preset-expo", { jsxImportSource: "@bacons/mdx/jsx" }]],
};
};
Now when you render a div, p, h1, etc. on native, you will get a helpful error message.
export default function App() {
return <div>Hey</div>;
}
ERROR Unsupported DOM <p /> at: /Users/evanbacon/Documents/GitHub/bacons/mdx/apps/demo/src/App.tsx:1:11
This will break in production.
Web-only components
It's possible to parse MDX to DOM elements instead of universal components. This can be useful when building for web-only or migrating from web-only. To do this, pull in the getDOMComponents
function and pass it to the components
prop of the MDX component.
import { getDOMComponents } from "@bacons/mdx";
import Demo from "./readme.md";
export default function App() {
return <Demo components={getDOMComponents()} />;
}
This will render the following MDX as DOM elements:
# Hello World
I **am** a _markdown_ file!
And the DOM:
<h1>Hello World</h1>
<p>I <strong>am</strong> a <em>markdown</em> file!</p>
Next.js Usage
- Follow the steps detailed here: https://nextjs.org/docs/advanced-features/using-mdx
- Add the following packages to
transpile-modules
within yournext.config.js
:'@bacons/mdx', '@bacons/react-views', '@expo/html-elements',
Known Issues
- ol, li, ul are all buggy. PRs welcome.
- Native image ratios are weird.
About this project
This is a universal MDX implementation for Expo (React & Metro). It aims to be a general-purpose MDX implementation for Expo projects that leverage universal Metro (Expo CLI).
- Test in the
apps/demo
project.
This library powers my (Evan Bacon) personal blog, the source can be found here: Evan Bacon portfolio.