ghost/core/server/helpers/reading_time.js

// # Reading Time Helper
//
// Usage:  `{{reading_time}}`
// or for translatable themes, with (t) translation helper's subexpressions:
// `{{reading_time seconds=(t "< 1 min read") minute=(t "1 min read") minutes=(t "% min read")}}`
// and in the theme translation file, for example Spanish es.json:
// "< 1 min read": "< 1 min de lectura",
// "1 min read": "1 min de lectura",
// "% min read": "% min de lectura",
//
// Returns estimated reading time for post

const proxy = require('./proxy');
const _ = require('lodash');
const schema = require('../data/schema').checks;
const SafeString = proxy.SafeString;
const countImages = require('@tryghost/helpers').utils.countImages;
const countWords = require('@tryghost/helpers').utils.countWords;

module.exports = function reading_time(options) {// eslint-disable-line camelcase
    options = options || {};
    options.hash = options.hash || {};

    var html,
        wordsPerMinute = 275,
        wordsPerSecond = wordsPerMinute / 60,
        wordCount,
        imageCount,
        readingTimeSeconds,
        readingTimeMinutes,
        readingTime,
        minute = _.isString(options.hash.minute) ? options.hash.minute : '1 min read',
        minutes = _.isString(options.hash.minutes) ? options.hash.minutes : '% min read';

    // only calculate reading time for posts
    if (!schema.isPost(this)) {
        return null;
    }

    html = this.html;
    imageCount = this.feature_image ? 1 : 0;
    imageCount += countImages(html);
    wordCount = countWords(html);
    readingTimeSeconds = wordCount / wordsPerSecond;

    for (var i = 12; i > 12 - imageCount; i -= 1) {
        // add 12 seconds for the first image, 11 for the second, etc. limiting at 3
        readingTimeSeconds += Math.max(i, 3);
    }

    readingTimeMinutes = Math.round(readingTimeSeconds / 60);

    if (readingTimeMinutes <= 1) {
        readingTime = minute;
    } else {
        readingTime = minutes.replace('%', readingTimeMinutes);
    }

    return new SafeString(readingTime);
};