ecoindex.js

var domQuantiles = [0, 47, 75, 159, 233, 298, 358, 417, 476, 537, 603, 674, 753, 843, 949, 1076, 1237, 1459, 1801, 2479, 594601];
var reqQuantiles = [0, 2, 15, 25, 34, 42, 49, 56, 63, 70, 78, 86, 95, 105, 117, 130, 147, 170, 205, 281, 3920];
var sizeQuantiles = [0, 1.37, 144.7, 319.53, 479.46, 631.97, 783.38, 937.91, 1098.62, 1265.47, 1448.32, 1648.27, 1876.08, 2142.06, 2465.37, 2866.31, 3401.59, 4155.73, 5400.08, 8037.54, 223212.26];

/**
 * @param {array} quantiles
 * @param {number} value
 * @return {number}
 */
var calculateIndex = function (quantiles, value) {
    for (var i = 1; i < quantiles.length; i++) {
        if (value < quantiles[i]) {
			return (i - 1 + (value - quantiles[i - 1]) / (quantiles[i] - quantiles[i - 1]));
        }
    }

    return quantiles.length - 1;
};

/**
 * @param {number} dom Number of DOM elements
 * @param {number} req Number of HTTP requests
 * @param {number} size Page size in ko
 * @return {number}
 */
var getScore = function (dom, req, size) {
    var domIndex = calculateIndex(domQuantiles, dom),
        reqIndex = calculateIndex(reqQuantiles, req),
        sizeIndex = calculateIndex(sizeQuantiles, size),
        total = 100 - 5 * (3 * domIndex + 2 * reqIndex + sizeIndex) / 6;

    return Math.round(total);
};

/**
 * @param {number} score EcoIndex score
 * @return {string}
 */
var getGrade = function (score) {
    switch (true) {
        case score >= 75:
            return 'A';
        case score >= 65:
            return 'B';
        case score >= 50:
            return 'C';
        case score >= 35:
            return 'D';
        case score >= 20:
            return 'E';
        case score >= 5:
            return 'F';
        default:
            return 'G';
    }
};

/**
 * @param {number} score EcoIndex score
 * @return {number}
 */
var getGreenhouseGasEmission = function (score) {
    return Math.round(100 * (2 + 2 * (50 - score) / 100)) / 100;
};

/**
 * @param {number} score EcoIndex score
 * @return {number}
 */
var getWaterConsumption = function (score) {
    return Math.round(100 * (3 + 3 * (50 - score) / 100)) / 100;
};

/**
 * @param {number} dom Number of DOM elements
 * @param {number} req Number of HTTP requests
 * @param {number} size Page size in ko
 * @return {number}
 */
module.exports.getEcoindex = function (dom, req, size) {
	var score = getScore(dom, req, size);

    return {
		score: score,
		grade: getGrade(score),
		ghg: getGreenhouseGasEmission(score),
		water: getWaterConsumption(score),
	}
};

/**
 * @deprecated
 */
module.exports.calculate = function (dom, req, size) {
	console.debug('[Notice] The method "ecoindex.calculate()" is deprecated since version 1.3 and will be removed in version 2.0. Use "ecoindex.getEcoindex()" instead.');

    return getScore(dom, req, size);
};

/**
 * @deprecated
 */
module.exports.getNote = function (index) {
	console.debug('[Notice] The method "ecoindex.getNote()" is deprecated since version 1.3 and will be removed in version 2.0. Use "ecoindex.getEcoindex()" instead.');

    return getGrade(index);
};