This code can be used as an eleventy filter to create the reading time (in minutes) of a piece of content.

readingtime.js

/*
 * Calculate the reading time, in minutes, of a post
 *
 * Assumptions:
 * - average reading time is 240 words per minute
 *   source: https://bit.ly/3HCogSr, "Most Comprehensive
 *   Review To Date Finds The Average Person’s Reading
 *   Speed Is Slower Than Previously Thought"
 *
 * Output:
 * - reading time is rounded to the nearest minute
 * - in the case of less than 1 minute, reading time is
 *   displayed as "less than a minute"
 *
 * @param {String} text
 */

module.exports = function (text) {
  var content = new String(text);
  const speed = 240; // reading speed in words per minute

  // remove all html elements
  var re = /(&lt;.*?&gt;)|(<[^>]+>)/gi;
  var plain = content.replace(re, "");

  // replace all newlines and 's with spaces
  var plain = plain.replace(/\s+|'s/g, " ");

  // create array of all the words in the post & count them
  var words = plain.split(" ");
  var count = words.length;

  // calculate the reading time
  var readingTime = Math.round(count / speed);
  if (readingTime === 0) {
    return "Less than 1 minute to read";
  } else if (readingTime === 1) {
    return "1 minute to read";
  } else {
    return readingTime + " minutes to read";
  }
};

Cool. Thanks for the link to regex101. Looks very handy. I'm going to make an update to my Calculating blog using your suggestions (at some point). Right now, I'm scouring the net for the next issue of The 11ty Bundler. I am thinking that if I continue to generate the Bundler, it will probably turn into its own website. I broke down and bought the 11tybundler.com domain yesterday. Not that that necessarily signals commitment as I have a handful of other unused domains that started as ideas in my head. At least with this one, I've already started something that could make more sense for me to head down that path. What I like about the idea is that it will give me more reasons to keep learning about Eleventy, JS, and CSS.

Sounds like a great idea to me. I look forward to reading more, if you do put together more issues (so to speak). 😊

This gist has been updated with the help of @Aankhen. Many thanks. The resulting word counts are comparable to the earlier regex I used.