Hugo: compare dates to flag old content

With the recent redesign of my website I also wanted to add a note to old articles. The IT world is changing fast and information can quickly be outdated, so I decided to add an automatically generated note to every post that is older than 4 years. Using the Hugo Math function and Date values it can be accomplished in automated-enough fashion.

Partial

First I created a new partial named single-header.html and added it to all my single.html templates. The file contains the following code which I will explain step by step.

<section class="age-note">
    <h2>ATTENTION!</h2>
    <p>This article is over 4 years old, it may be outdated!</p>
</section>

The magic all happens in the first 2 lines. First the "now" time is retrieved, this is the build time - not the current time when the page is loaded in the browser. Then we calculate the different using the Hugo built-in sub function, giving the two dates in year format (2020, 2015, ...) as arguments.

$article_age := sub $now (int (.Date.Format "2006"))
# For an aricle written in 2013 the code looks like
# $article_age = sub 2020 2013

After filling in all variables and doing the subtraction, the $article_age variable contains an integer, like 7 or 3. The next line of code checks if the number $article_age is greater than 4, which means the article is older than 4 years. If this is true, the note is displayed.

    $article_age is greater than 4

Because we are doing a gt (greater than) comparison only articles that are older than 4 years (5 and more) will be flagged.

See it in action

A live example can be seen on my page, for example in the oldest post "Hello world" or in any post from 2015 and before.