yoastseo/build/languageProcessing/researches/getFleschReadingScore.js

Yoast client-side content analysis

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.DIFFICULTY = void 0;
exports.default = _default;
var _stripNumbers = _interopRequireDefault(require("../helpers/sanitize/stripNumbers.js"));
var _countSentences = _interopRequireDefault(require("../helpers/sentence/countSentences.js"));
var _countWords = _interopRequireDefault(require("../helpers/word/countWords.js"));
var _countSyllables = _interopRequireDefault(require("../helpers/syllables/countSyllables.js"));
var _lodash = require("lodash");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/** @module analyses/calculateFleschReading */

/**
 * Calculates an average from a total and an amount
 *
 * @param {number} total The total.
 * @param {number} amount The amount.
 * @returns {number} The average from the total and the amount.
 */
const getAverage = function (total, amount) {
  return total / amount;
};

/**
 * The Flesch reading ease difficulty.
 * @readonly
 * @enum {number}
 */
const DIFFICULTY = exports.DIFFICULTY = {
  NO_DATA: -1,
  VERY_EASY: 0,
  EASY: 1,
  FAIRLY_EASY: 2,
  OKAY: 3,
  FAIRLY_DIFFICULT: 4,
  DIFFICULT: 5,
  VERY_DIFFICULT: 6
};

/**
 * Returns the Flesch reading ease difficulty based on the boundaries
 * defined in the score configuration.
 *
 * @param {number} score The Flesch reading ease score.
 * @param {Object} scoreConfiguration The score configuration.
 *
 * @returns {DIFFICULTY} The Flesch reading ease difficulty.
 */
function getDifficulty(score, scoreConfiguration) {
  if (score >= scoreConfiguration.borders.veryEasy) {
    return DIFFICULTY.VERY_EASY;
  } else if ((0, _lodash.inRange)(score, scoreConfiguration.borders.easy, scoreConfiguration.borders.veryEasy)) {
    return DIFFICULTY.EASY;
  } else if ((0, _lodash.inRange)(score, scoreConfiguration.borders.fairlyEasy, scoreConfiguration.borders.easy)) {
    return DIFFICULTY.FAIRLY_EASY;
  } else if ((0, _lodash.inRange)(score, scoreConfiguration.borders.okay, scoreConfiguration.borders.fairlyEasy)) {
    return DIFFICULTY.OKAY;
  } else if ((0, _lodash.inRange)(score, scoreConfiguration.borders.fairlyDifficult, scoreConfiguration.borders.okay)) {
    return DIFFICULTY.FAIRLY_DIFFICULT;
  } else if ((0, _lodash.inRange)(score, scoreConfiguration.borders.difficult, scoreConfiguration.borders.fairlyDifficult)) {
    return DIFFICULTY.DIFFICULT;
  }
  return DIFFICULTY.VERY_DIFFICULT;
}

/**
 * Retrieves the scoring configuration defining the boundaries to use to
 * determine the Flesch reading ease difficulty.
 *
 * @param {Researcher} researcher The researcher.
 *
 * @returns {Object} The language specific scoring configuration, or the default configuration if not available.
 */
function getConfiguration(researcher) {
  const languageSpecificConfig = researcher.getConfig("fleschReadingEaseScores");
  const defaultConfig = {
    borders: {
      veryEasy: 90,
      easy: 80,
      fairlyEasy: 70,
      okay: 60,
      fairlyDifficult: 50,
      difficult: 30,
      veryDifficult: 0
    },
    scores: {
      veryEasy: 9,
      easy: 9,
      fairlyEasy: 9,
      okay: 9,
      fairlyDifficult: 6,
      difficult: 3,
      veryDifficult: 3
    }
  };
  return languageSpecificConfig ? languageSpecificConfig : defaultConfig;
}

/**
 * This calculates the Flesch reading score for a given text.
 *
 * @param {Paper}       paper           The paper containing the text.
 * @param {Researcher}  researcher      The researcher.
 *
 * @returns {{ score: number, difficulty: DIFFICULTY }} The Flesch reading score.
 */
function _default(paper, researcher) {
  const syllables = researcher.getConfig("syllables");
  const memoizedTokenizer = researcher.getHelper("memoizedTokenizer");
  const languageSpecificConfiguration = getConfiguration(researcher);
  let text = paper.getText();
  if (text === "") {
    // A score of -1 signals to the code down the line that no valid FRE was calculated.
    return {
      score: -1,
      difficulty: DIFFICULTY.NO_DATA
    };
  }
  text = (0, _stripNumbers.default)(text);
  const numberOfSentences = (0, _countSentences.default)(text, memoizedTokenizer);
  const numberOfWords = (0, _countWords.default)(text);

  // Do not show the Flesch reading ease when there is not enough data for the FRE to make sense. Also used to prevent division by zero errors.
  // A score of -1 signals to the code down the line that no valid FRE was calculated.
  if (numberOfSentences < 1 || numberOfWords <= 10) {
    return {
      score: -1,
      difficulty: DIFFICULTY.NO_DATA
    };
  }
  const numberOfSyllables = (0, _countSyllables.default)(text, syllables);
  const averageWordsPerSentence = getAverage(numberOfWords, numberOfSentences);
  const syllablesPer100Words = numberOfSyllables * (100 / numberOfWords);
  const statistics = {
    numberOfSentences,
    numberOfWords,
    numberOfSyllables,
    averageWordsPerSentence,
    syllablesPer100Words
  };
  const getScore = researcher.getHelper("fleschReadingScore");
  const score = (0, _lodash.clamp)(getScore(statistics), 0, 100);
  const difficulty = getDifficulty(score, languageSpecificConfiguration);
  return {
    score,
    difficulty
  };
}
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