Reading time estimation

[sbrl]

It would be cool if we could have a configurable setting to display the estimated reading time for a page. Firefox's reader mode does this already, and with some effort I've tracked down the algorithm they use.

The relevant lines are as follows:

  _assignReadTime(article) {
    let lang = article.language || "en";
    const readingSpeed = this._getReadingSpeedForLanguage(lang);
    const charactersPerMinuteLow = readingSpeed.cpm - readingSpeed.variance;
    const charactersPerMinuteHigh = readingSpeed.cpm + readingSpeed.variance;
    const length = article.length;

    article.readingTimeMinsSlow = Math.ceil(length / charactersPerMinuteLow);
    article.readingTimeMinsFast = Math.ceil(length / charactersPerMinuteHigh);
  },

  /**
   * Returns the reading speed of a selection of languages with likely variance.
   *
   * Reading speed estimated from a study done on reading speeds in various languages.
   * study can be found here: http://iovs.arvojournals.org/article.aspx?articleid=2166061
   *
   * @return object with characters per minute and variance. Defaults to English
   *         if no suitable language is found in the collection.
   */
  _getReadingSpeedForLanguage(lang) {
    const readingSpeed = new Map([
      ["en", { cpm: 987, variance: 118 }],
      ["ar", { cpm: 612, variance: 88 }],
      ["de", { cpm: 920, variance: 86 }],
      ["es", { cpm: 1025, variance: 127 }],
      ["fi", { cpm: 1078, variance: 121 }],
      ["fr", { cpm: 998, variance: 126 }],
      ["he", { cpm: 833, variance: 130 }],
      ["it", { cpm: 950, variance: 140 }],
      ["jw", { cpm: 357, variance: 56 }],
      ["nl", { cpm: 978, variance: 143 }],
      ["pl", { cpm: 916, variance: 126 }],
      ["pt", { cpm: 913, variance: 145 }],
      ["ru", { cpm: 986, variance: 175 }],
      ["sk", { cpm: 885, variance: 145 }],
      ["sv", { cpm: 917, variance: 156 }],
      ["tr", { cpm: 1054, variance: 156 }],
      ["zh", { cpm: 255, variance: 29 }],
    ]);

We might want to reverse-engineer Firefox's reader mode to make sure our estimate is hidden though when you enter reader mode too.

Perhaps adding some settings like reading_time_display and reading_time_language would work.

Adding a note to the credits might be a good idea too.

[sbrl]

Done :D