Filter Posts by Tag

Blogs can quickly become disorganized. You might want to link to a page on your website which only lists posts about CSS. With a bit of javascript, you can use /blog?tag=css to filter your posts.

⚠️ For the following method to work, each post item should have a data attribute of data-tags="[tag1,tag2]">.

First, we need to find our posts. Use the document.querySelectorAll method[^1]. The method takes one parameter: A selector string formatted like a css selector. Now, we need to get the tag in the url. The global location.search variable provides us with the query parameters at the end of the url. This will give us a string, such as ?topic=css, which we can manipulate to find the tag.

Find which posts don't have the tag. For each post, check if the tags in the data-tags attribute include the one we found in the url. (Hint: use Array.filter) Then, hide the filtered posts. HTML has a handy hidden attribute for situations like this. Set the hidden attribute of each filtered post to true.

You can now filter your blog posts by tag. Here's the full snippet.

<ul>
  <li class="post">
      <!-- contents -->
  </li>
 <!-- more -->
</ul>

// Select all posts
const posts = [...document.querySelectorAll(".post")];

// Get the tag in the url
const tag = location.search.slice(location.search.indexOf("=") + 1);

if(tag) {
    // Find which posts don’t have the tag
    let postsNoTag = posts.filter(l => {
        return JSON.parse(l.dataset.tags).includes(tag) === false;
    });

	// Hide all posts which don’t have the tag
    postsNoTag.forEach(p => {
        p.setAttribute("hidden", true);
    });
}

[^1]: For more details, see this page on MDN.