How to add an estimated reading time in AstroPaper

As the Astro docs say, we can use remark plugin to add a reading time property in our frontmatter. However, for some reason, we can’t add this feature by following what stated in Astro docs. Therefore, to achieve this, we have to tweak a little bit. This post will demonstrate how we can do that.

Open Table of contents

Add reading time in PostDetails
Access reading time outside of PostDetails (optional)
Displaying reading time (optional)
Conclusion

Add reading time in PostDetails

Step (1) Install required dependencies.

npm install reading-time mdast-util-to-string

Step (2) Create remark-reading-time.mjs file under utils directory

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);
    data.astro.frontmatter.readingTime = readingTime.text;
  };
}

Step (3) Add the plugin to astro.config.ts

import { remarkReadingTime } from "./src/utils/remark-reading-time.mjs"; // make sure your relative path is correct

// https://astro.build/config
export default defineConfig({
  site: SITE.website,
  integrations: [
    // other integrations
  ],
  markdown: {
    remarkPlugins: [
      remarkToc,
      remarkReadingTime, // 👈🏻 our plugin
      [
        remarkCollapse,
        {
          test: "Table of contents",
        },
      ],
    ],
    // other config
  },
  // other config
});

Step (4) Add readingTime to blog schema (src/content/config.ts)

import { SITE } from "@config";
import { defineCollection, z } from "astro:content";

const blog = defineCollection({
  type: "content",
  schema: ({ image }) =>
    z.object({
      // others...
      canonicalURL: z.string().optional(),
      readingTime: z.string().optional(), // 👈🏻 readingTime frontmatter
    }),
});

export const collections = { blog };

Step (5) Create a new file called getPostsWithRT.ts under src/utils directory.

import type { MarkdownInstance } from "astro";
import type { CollectionEntry } from "astro:content";
import { slugifyStr } from "./slugify";

export const getReadingTime = async () => {
  // Get all posts using glob. This is to get the updated frontmatter
  const globPosts = import.meta.glob("../content/blog/*.md") as Promise<
    CollectionEntry<"blog">["data"][]
  >;

  // Then, set those frontmatter value in a JS Map with key value pair
  const mapFrontmatter = new Map();
  const globPostsValues = Object.values(globPosts);
  await Promise.all(
    globPostsValues.map(async globPost => {
      const { frontmatter } = await globPost();
      mapFrontmatter.set(
        slugifyStr(frontmatter.title),
        frontmatter.readingTime
      );
    })
  );

  return mapFrontmatter;
};

const getPostsWithRT = async (posts: CollectionEntry<"blog">[]) => {
  const mapFrontmatter = await getReadingTime();
  return posts.map(post => {
    post.data.readingTime = mapFrontmatter.get(slugifyStr(post.data.title));
    return post;
  });
};

export default getPostsWithRT;

Step (6) Refactor getStaticPaths of /src/pages/posts/[slug].astro as the following

---
// other imports
import getPostsWithRT from "@utils/getPostsWithRT";

export interface Props {
  post: CollectionEntry<"blog">;
}

export async function getStaticPaths() {
  const posts = await getCollection("blog", ({ data }) => !data.draft);

  const postsWithRT = await getPostsWithRT(posts); // replace reading time logic with this func

   const postResult = postsWithRT.map(post => ({ // make sure to replace posts with postsWithRT
    params: { slug: post.slug },
    props: { post },
  }));

// other codes

Step (7) Refactor PostDetails.astro like this. Now you can access and display readingTime in PostDetails.astro

---
// imports

export interface Props {
  post: CollectionEntry<"blog">;
}

const { post } = Astro.props;

const {
  title,
  author,
  description,
  ogImage,
  readingTime, // we can now directly access readingTime from frontmatter
  pubDatetime,
  modDatetime,
  tags } = post.data;

// other codes
---

Access reading time outside of PostDetails (optional)

By following the previous steps, you can now access readingTime frontmatter property in you post details page. Sometimes, this is exactly what you want. If so, you can skip to the next section. However, if you want to display “estimated reading time” in index, posts, and technically everywhere, you need to do the following extra steps.

Step (1) Update utils/getSortedPosts.ts as the following

import type { CollectionEntry } from "astro:content";
import getPostsWithRT from "./getPostsWithRT";

const getSortedPosts = async (posts: CollectionEntry<"blog">[]) => {
  // make sure that this func is async
  const postsWithRT = await getPostsWithRT(posts); // add reading time
  return postsWithRT
    .filter(({ data }) => !data.draft)
    .sort(
      (a, b) =>
        Math.floor(
          new Date(b.data.modDatetime ?? b.data.pubDatetime).getTime() / 1000
        ) -
        Math.floor(
          new Date(a.data.modDatetime ?? a.data.pubDatetime).getTime() / 1000
        )
    );
};

export default getSortedPosts;

Step (2) Make sure to refactor every file which uses getSortedPosts function. You can simply add await keyword in front of getSortedPosts function.

Files that use getSortedPosts function are as follow

src/pages/index.astro
src/pages/posts/index.astro
src/pages/rss.xml.ts
src/pages/posts/index.astro
src/pages/posts/[slug].astro
src/utils/getPostsByTag.ts

All you have to do is like this

const sortedPosts = getSortedPosts(posts); // old code ❌
const sortedPosts = await getSortedPosts(posts); // new code ✅

Now you can access readingTime in other places besides PostDetails

Displaying reading time (optional)

Since you can now access readingTime in your post details (or everywhere if you do the above section), it’s up to you to display readingTime wherever you want.

But in this section, I’m gonna show you how I would display readingTime in my components. This is optional. You can ignore this section if you want.

Step (1) Update Datetime component to display readingTime

import { LOCALE } from "@config";

export interface Props {
  datetime: string | Date;
  size?: "sm" | "lg";
  className?: string;
  readingTime?: string; // new type
}

export default function Datetime({
  datetime,
  size = "sm",
  className,
  readingTime, // new prop
}: Props) {
  return (
    // other codes
    <span className={`italic ${size === "sm" ? "text-sm" : "text-base"}`}>
      <FormattedDatetime pubDatetime={pubDatetime} modDatetime={modDatetime} />
      <span> ({readingTime})</span> {/* display reading time */}
    </span>
    // other codes
  );
}

Step (2) Then, pass readingTime props from its parent component.

file: Card.tsx

export default function Card({ href, frontmatter, secHeading = true }: Props) {
  const { title, pubDatetime, modDatetime description, readingTime } = frontmatter;
  return (
    ...
    <Datetime
      pubDatetime={pubDatetime}
      modDatetime={modDatetime}
      readingTime={readingTime}
    />
    ...
  );
}

file: PostDetails.tsx

// Other Codes
<main id="main-content">
  <h1 class="post-title">{title}</h1>
  <Datetime
    pubDatetime={pubDatetime}
    modDatetime={modDatetime}
    size="lg"
    className="my-2"
    readingTime={readingTime}
  />
  {/* Other Codes */}
</main>
// Other Codes

Conclusion

By following the provided steps and tweaks, you can now incorporate this useful feature into your content. I hope this post helps you adding readingTime in your blog. AstroPaper might include reading time by default in future releases. 🤷🏻‍♂️

Kyay Zuu for Reading 🙏🏻