Calculating Read time in JavaScript

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Note: This blog was originally published on my website.

This is a very simple task. First, we need a sentence to try this out. Let's use "The quick brown fox jumps over the lazy dog". A few thing we need to know is:

  • The average word is 5 in the English dictionary.
  • The average Words Per Minute for reading (WPM) is 200-250, which averages to 225 WPM. (https://archive.is/FRfWJ).

So, we have to split the text every 5 letters and divide it by 225 WPM. This can easily be done with JavaScript:

"The quick brown fox jumps over the lazy dog.".match(/.{1,5}/g).length/225;

Which should return a value of 0.04. So are we done? No. We also need make it human readable. First we need to round to the nearest whole number by using Math.round() :

Math.round("The quick brown fox jumps over the lazy dog.".match(/.{1,5}/g).length/225);

Which should return 0. Now we are almost done. Let's make it human readable. We can give it summaries using if/else statements.

Lets use:

  • Less than a minute read - for read times under a minute.
  • n min read - for read times that are over a minute.

as statements.

var rt = Math.round("The quick brown fox jumps over the lazy dog.".match(/.{1,5}/g).length/225);
  if (rt <= 0) {
  rt = "Less than a minute read."
  } else if (rt === 1){
  rt = `${rt} min read.`
  } else if (isNaN(rt)){
  rt = "Failed to calculate readtime!"
  } else {
  rt = "Failed to calculate readtime!"
  }

which returns Less than a minute read.

Let's make it ready for "production" by wrapping it around a function and compressing it using JScompress. I put the source code on P2Pbin, which you can find here.

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