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Cover image for Building React Components from headless CMS markdown
Stefan Kudla
Stefan Kudla

Posted on • Originally published at cosmicjs.com

Building React Components from headless CMS markdown

Markdown has become a staple in my workflow as a developer and content creator. It’s quick to write, flexible with its features, and has easy-to-remember syntax.

Using React Markdown, we’re going to create Custom React Components (in a Next.js application) using parsed markdown retrieved from a headless CMS. By doing so, we will be able to quite easily utilize cutting-edge features like Next Image in the body of our Markdown. This way, we can take dynamic content and shape it the way we want, improving performance, accessibility, and overall user experience.

mdn to html

This article features the Next.js Developer Portfolio Template I built with Cosmic. You can follow along by visiting the App Template Page and importing the template into your own Cosmic Bucket (create an account if you’d like to follow along this way and haven’t already made one). Or, view the source code if you’d rather follow along with your own application.

A brief overview of React Markdown

React Markdown is a React Component to render markdown which lets you create and render custom components instead of standard HTML components. It is safe by default (no dangerouslySetInnerHTML) and allows you to use a wide array of plugins from remarkjs to enhance your markdown.

Diagram of the react markdown architecture flow

To further understand this component, let’s reference the diagram above step-by-step.

  1. The markdown content is parsed and turned into a markdown syntax tree
  2. The markdown syntax tree is transformed to an HTML syntax tree through remark
  3. The HTML syntax tree is transformed through rehype, and rendered to React components.

Installing the packages

To use react-markdown, we only need the package itself.

pnpm add react-markdown
## or
npm install react-markdown
## or
yarn add react-markdown
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To retrieve our data from Cosmic, we can install the Cosmic NPM module.

pnpm add cosmicjs
## or
npm install cosmicjs
## or
yarn add cosmicjs
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Getting our Markdown content from a headless CMS

In this example, we’re retrieving markdown content from a Cosmic Object that is going to be the body of text for an article. Within the pages directory of our Next.js application, make sure you have a [slug].jsx file created within a folder called posts, articles , or whatever you please.

We can import the cosmicjs package, set the environment variables, then write two functions that will get data from our Cosmic dashboard.

const Cosmic = require('cosmicjs')
const api = Cosmic()

const bucket = api.bucket({
  slug: process.env.COSMIC_BUCKET_SLUG,
  read_key: process.env.COSMIC_READ_KEY,
})

export async function getAllPostsWithSlug() {
  const params = {
    query: { type: 'posts' },
    props: 'title,slug,metadata,created_at',
  }
  const data = await bucket.getObjects(params)
  return data.objects
}

export async function getPostAndMorePosts(slug, preview) {
  const singleObjectParams = {
    query: { slug: slug },
    ...(preview && { status: 'any' }),
    props: 'slug,title,metadata,created_at',
  }
  const moreObjectParams = {
    query: { type: 'posts' },
    ...(preview && { status: 'any' }),
    limit: 3,
    props: 'title,slug,metadata,created_at',
  }

  try {
    const data = await bucket.getObjects(singleObjectParams)
    const moreObjects = await bucket.getObjects(moreObjectParams)
    const morePosts = moreObjects.objects
      ?.filter(({ slug: object_slug }) => object_slug !== slug)
      .slice(0, 2)
    return {
      post: data?.objects[0],
      morePosts,
    }
  } catch (error) {
    if (is404(error)) return
    throw error
  }
}
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Within our [slug].jsx file, we can call getStaticProps() and getStaticPaths() , pull in data, then pass it through to our Post component.

// pages/posts/[slug].jsx

const Post = ({ post }) => {
  return (
    <>
      <article>
        <PostBody content={post.metadata.content} />
      </article>
    </>
  )
}
export default Post

export async function getStaticProps({ params, preview = null }) {
  const data = await getPostAndMorePosts(params.slug, preview)

  return {
    props: {
      preview,
      post: {
        ...data.post,
      },
      morePosts: data.morePosts || [],
    },
  }
}

export async function getStaticPaths() {
  const allPosts = (await getAllPostsWithSlug()) || []
  return {
    paths: allPosts.map(post => `/posts/${post.slug}`),
    fallback: true,
  }
}
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Now that we’ve got the page itself set up, let’s dive into our PostBody component, where we will be using react-markdown to render our content.

Implementing React Markdown

Within our PostBody we can import and use the ReactMarkdown Component. We simply import the package and wrap our content in the ReactMarkdown component.

import ReactMarkdown from 'react-markdown'

const PostBody = ({ content }) => {
  return (
    <div className="max-w-2xl mx-auto">
      <ReactMarkdown>
        {content}
      </ReactMarkdown>
    </div>
  )
}
export default PostBody
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Creating custom components

Furthermore, we can create custom components. To do this, we will create a components object above our PostBody component and pass it through to the ReactMarkdown component.

When creating the custom components, the key will be the HTML equivalent for the content we write in markdown. The parameter will be what you want to render as an HTML element, and will have access to the props of that element. For example, the a element will give us access to href and children and the img tag src and alt.

The JSX you write within these functions will return the provided element. You could write something like h1: h1 => {return (<h2>{h1.children}</h2>)} and you will render h2 elements for every h1 written in markdown.

import ReactMarkdown from 'react-markdown'

const components = {
  a: a => {
    return (
      <a href={a.href} rel="noopener noreferrer" target="_blank">
        {a.children}
      </a>
    )
  },
}

const PostBody = ({ content }) => {
  return (
    <div className="max-w-2xl mx-auto">
      <ReactMarkdown
        components={components}
      >
        {content}
      </ReactMarkdown>
    </div>
  )
}
export default PostBody
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My favorite use case so far has been implementing Next Image for optimized image sizes and better page load times.

Without using Next Image, having lots of images in our markdown will require all of the images to be loading when the page is requested. This is slow and negatively impacts user experience and lighthouse scores.

When I refresh the page, all of the images will be loaded at once. Yikes!

Loading all images on a web page without lazy loading

Let’s improve this! Import Image from next/image, then create a custom img component inside of the components object. Remember, we have access to some standard props with these components, so we can simply grab the src and alt from the img. We pass them into our Image component written in our JSX, defining a set height and width, a lower quality to the file size, and a layout of responsive to serve scaled images according to screen size, ensuring that small devices don’t receive any unnecessarily large file sizes.

import ReactMarkdown from 'react-markdown'
import Image from 'next/image'

const components = {
  a: a => {
    return (
      <a href={a.href} rel="noopener noreferrer" target="_blank">
        {a.children}
      </a>
    )
  },
  img: img => {
    return (
      <Image
        src={img.src}
        alt={img.alt}
        width={400}
        height={300}
        quality={50}
        layout="responsive"
        objectFit="contain"
        objectPosition="center"
      />
    )
  },
}

const PostBody = ({ content }) => {
  return (
    <div className="max-w-2xl mx-auto">
      <ReactMarkdown
        components={components}
      >
        {content}
      </ReactMarkdown>
    </div>
  )
}
export default PostBody
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Now that we’ve added the custom Image component, let’s reload the page and see the magic.

Loading images on a web page with Next Image and lazy loading

We are no longer requesting all of those images at once, and as we scroll down the page, the lazy loaded images start to appear in the network tab.

Having the flexibility to create custom React Components for markdown is essential and with react-markdown, we can achieve this in just a few lines of code. Boosting performance, increasing link security, and having overall increased capabilities for our markdown data are what we achieve here. Aside from the improvements within our application, this component is super easy to use and taps us into the unifiedjs (giving us superpowers!).

Come build some cool sh!t with us! You can tune into our new show Build Time, where we cover topics like headless CMS, Next.js, React, and many many more.

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