Linear Regression - Getting R Squared in javascript

rsquared.js

/**
 * 
 * @param {Function} predict 
 * @param {Array} data 
 * @returns {Object} 
 */
function getRSquared(predict, data) {
    var yAxis = data;
    var rPrediction = [];

    var meanValue = 0; // MEAN VALUE
    var SStot = 0; // THE TOTAL SUM OF THE SQUARES
    var SSres = 0; // RESIDUAL SUM OF SQUARES
    var rSquared = 0;

    // SUM ALL VALUES
    for (var n in yAxis) { meanValue += yAxis[n]; }

    // GET MEAN VALUE
    meanValue = (meanValue / yAxis.length);
    
    for (var n in yAxis) { 
        // CALCULATE THE SSTOTAL    
        SStot += Math.pow(yAxis[n] - meanValue, 2); 
        // REGRESSION PREDICTION
        rPrediction.push(predict(n));
        // CALCULATE THE SSRES
        SSres += Math.pow(rPrediction[n] - yAxis[n], 2);
    }

    // R SQUARED
    rSquared = 1 - (SSres / SStot);

    return {
        meanValue: meanValue,
        SStot: SStot,
        SSres: SSres,
        rSquared: rSquared
    };
}

var result = getRSquared((x) => { return (6 * x) - 5 }, [0, 1, 4, 9, 16, 25, 36]);