Hexo: Previous and Next Posts Within a Category

In the “Book” theme, I treat each category as a book, and posts inside the category as chapters.

In that case, you can’t just use site‑wide posts for previous/next navigation.

So based on Hexo: Output Posts by Category - 折影轻梦 (nexmoe.com), I wrote a snippet to output previous/next posts within the same category.

Here’s the code (comments should make it clear):

<nav class="post-nav">
<% site.categories.map(function(category){  %>
    <% page.categories.map(function(page_category){ %>
        <% if(page_category.name == category.name){ %> <!-- Find the matching category -->
            <% let i = 0;%>
            <% category.posts.sort('-date').map(function(post){ %>
                <% i++;  %> 
                <% if(post.title == page.title){ %> <!-- Find current post index -->
                    <% let ix = 0;%>
                    <% category.posts.sort('-date').map(function(post){ %>
                        <% ix++; %> 
                        
                        <% if(ix == i + 1 && post.title){ %>  <!-- Previous post --> 
                            <div class="old">
                                <span>Previous</span>
                                <a href="<%- url_for(post.path) %>"> <%= post.title %></a>
                            </div>
                        <% } %>
                        
                        <% if(ix == i - 1 && post.title){ %> <!-- Next post --> 
                            <div class="new">
                                <span>Next</span>
                                <a href="<%- url_for(post.path) %>"> <%= post.title %></a>
                            </div>
                        <% } %>
                        
                    <% }) %>
                <% } %>
            <% }) %>
        <% } %>
    <% })%>
<% }) %>
</nav>

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