How to build a related posts component for your Next.js blog

Some blogs have these related articles or posts sections where visitors can have a preview at more content after they just read a post. That's what I wanted to create for my personal website which is built with Nextjs and in this article I want to show you how you also can do it for your own Next.js site or any other react application.

Related Posts Component

The keypoint to be able to show related Posts is that you somehow have to create a relation between the posts which doesn't exist yet. All my posts have

• a title,
• a description
• a date,
• tags and
• an image.

markdown
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---
title: "Post about Web-Development with React"
description: "This is a sample description for the post."
date: "2022-05-02"
tags: ["React", "Web-Development"]
image: "../image.jpg"
---

I decided to use the tags to create a relation between the posts because it's the only information which all posts can have in common and is related to the actual topic of the post. Therefore i needed data of all posts overall and data about the current posts. The data from the current post will be just passed as props to the component. All post data for my website is created in a CMS which can be accessed via GraphQL. The query to get allPosts looks like this.

javascript
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export async function getAllPosts() {
  const data = await fetchStrapiAPI(
    `
    {
      posts(sort: "published_at:desc") {
        id
        published_at
        title
        slug
        content
        excerpt
        tags {
          name
        }
        coverImage {
          url
        }
      }
    }
  `
  )
  return data?.posts
}

The only relevant information here is the slug and the tags with their names.

Now the current post gets filtered out from the posts array and a variable maxPosts for the maximum number of posts which should be displayed will be created.

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// filter out current post
let posts = allPosts.filter((aPost) => aPost.slug !==post.slug);
    
// define maxPosts to display
const maxPosts = 3

For better readability I assigned the tasks of the current posts to a variable called currentTags

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// get tags of current posts
const currentTags = post.tags.map((tag) => {
  return tag.name
})

Now you have to map through posts and the tags post.tags of these posts to check if one of these tags is the same as one of the currentTags. If one tag is the same we will just enumerate a new relevance variable.

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// rate posts depending on tags
    posts.forEach((post) => {
        post.relevance = 0
        post.tags.forEach((tag) => {
            if (currentTags.includes(tag.name)) {
                post.relevance ++
            }
        })
    })

The post with the highest relevance will be the post with the most common tags and be the most related post. If you are also using categories you can of course also adjust the relevance depending on the categories and the tags. For example you could add two relevance points for categories and one relevance point for tags.

Then you can sort the array of all posts descending by relevance.

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// sort posts by relevance
    const sortedPosts = posts.sort(function(a, b) {
        return b.relevance - a.relevance;
    });

In the end you can slice them with maxPosts and finally render them.

javascript
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import PostPreview from 'src/components/article/article-preview/article-preview'

export default function RecommendedPosts({ post, allPosts }) {

    // filter out current post
    let posts = allPosts.filter((aPost) => aPost.slug !==post.slug);
    
    // define maxPosts to display
    const maxPosts = 3

    // get tags of current posts
    const tags = post.tags.map((tag) => {
        return tag.name
    })

    // rate posts depending on tags
    posts.forEach((post) => {
        post.relevance = 0
        post.tags.forEach((tag) => {
            if (tags.includes(tag.name)) {
                post.relevance ++
            }
        })
    })

    // sort posts by relevance
    const sortedPosts = posts.sort(function(a, b) {
        return b.relevance - a.relevance;
    });

    return (
        <>
          {sortedPosts.slice(0,maxPosts).map((post, i) => (
            <PostPreview
              key={i} 
              postData={post}
            />
          ))}
        </>
    )
  }