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Adding reading time to Astro without the hassle

An alternative way to calculate reading time without full blog post rendering

Published onJanuary 03, 20242 minutes read

Table of Contents

Intro

I recently tried to move my website to Astro, but I wanted to keep most of the existing features.

As you can see in the blog page, the list of blog posts include the time it takes to read each post.

This feature in Astro requires quite a bit of work to be implemented.

The โ€œofficialโ€ way

If you followed the official docs recipe, first you need to install 2 packages:

yarn add -D reading-time mdast-util-to-string

Then, you create a custom Remark plugin to add the reading time to the frontmatter property of your blog posts.

remark-reading-time.mjs
import getReadingTime from 'reading-time';
import { toString } from 'mdast-util-to-string';
 
export function remarkReadingTime() {
  return function (tree, { data }) {
    const textOnPage = toString(tree);
    const readingTime = getReadingTime(textOnPage);
    // readingTime.text will give us minutes read as a friendly string,
    // i.e. "3 min read"
    data.astro.frontmatter.minutesRead = readingTime.text;
  };
}

And finally, you add it to your remark plugins array.

astro.config.mjs
import { defineConfig } from 'astro/config';
import { remarkReadingTime } from './remark-reading-time.mjs';
 
export default defineConfig({
  markdown: {
    remarkPlugins: [remarkReadingTime],
  },
});

The problem

By following these steps, you need to access the remarkPluginFrontmatter property from your post. And to do so, you first need to render the whole blog post content using the entry.render() function.

src/pages/posts/[slug].astro
---
...
 
const { entry } = Astro.props;
const { Content, remarkPluginFrontmatter } = await entry.render();
---
 
<html>
  <head>...</head>
  <body>
    ...
    <p>{remarkPluginFrontmatter.minutesRead}</p>
    ...
  </body>
</html>

Besides, as I told you before, I wanted to display this information in the blog posts list too, so it was a bit tedious to render the whole markdown for every post before being able to access the minutesRead property.

And even though I tried to do it this way, for some reason the minutesRead property was not really added to the frontmatter. Not sure if I did something wrong, but it simply didnโ€™t work for me.

My approach (or solution)

By doing a small modification to the custom Remark plugin originally suggested in Astro docs, I created an utility function to calculate the reading time.

It requires installing and using an additional dependency though:

yarn add -D mdast-util-from-markdown

It, instead of requiring rendering the blog post first, just takes the body property that already comes with the blog post entry.

src/utils/reading-time.ts
import calculateReadingTime from 'reading-time';
import { fromMarkdown } from 'mdast-util-from-markdown';
import { toString } from 'mdast-util-to-string';
 
export const getReadingTime = (text: string): string | undefined => {
  if (!text || !text.length) return undefined;
  try {
    const { minutes } = calculateReadingTime(toString(fromMarkdown(text)));
    if (minutes && minutes > 0) {
      return `${Math.ceil(minutes)} min read`;
    }
    return undefined;
  } catch (e) {
    return undefined;
  }
};

Now, you no longer need to add the custom Remark plugin to astro.config.mjs

astro.config.mjs
import { defineConfig } from 'astro/config';
- import { remarkReadingTime } from './remark-reading-time.mjs';
 
export default defineConfig({
  markdown: {
-    remarkPlugins: [...],
  },
});

Instead, use a BlogPost component in your blog page:

src/pages/blog.astro
---
import { getCollection } from 'astro:content';
import BlogPost from '@/components/blog/blog-post-item.astro';
 
// Get all `src/content/blog/` entries
const allBlogPosts = await getCollection('blog');
---
 
...
<ul>
  {
    allBlogPosts.map((post) => (
      <li><BlogPost post={post} /></li>
    ))
  }
</ul>
...

Then call the getReadingTime function from the component file and use that property anywhere:

src/components/blog-post-item.astro
---
import type { CollectionEntry } from 'astro:content';
 
import { getReadingTime } from '@/utils/reading-time';
 
interface Props {
  post: CollectionEntry<'blog'>;
}
 
const { post } = Astro.props;
 
// Calculate reading time using `body` property
const readingTime = getReadingTime(post.body);
---
 
...
<div>
  <a>
    <p>{post.title}</p>
  </a>
  <p>{readingTime}</p>
</div>
...

Conclusion

While the official Astro method works and is valid, it does require rendering each post.

A simpler alternative using existing data (the body property) and a custom utility function, avoids the extra step and is more efficient to calculate the reading time.

To summarize, by creating customized solutions, it is often possible to improve upon official methods by eliminating unnecessary steps. especially when your use case differs and you look for a more straightforward approach.