Calculating linear trend line for the chart components in JS

Display trend line is quite common problem while working with charts as front-end developer. Here I provide example of JS function for calculation linear trend line values and adding values to provided array of JSON values.

function(scores) {
    // Calculating the Slope (m) of the Trendline

    var count = scores.length;
    var ySum = 0, xSum = 0, xySum = 0, xSqSum = 0;
    $.each(scores, function( index, value ) {
        xSum += value.day;
        ySum += value.score;
        xySum += value.day * value.score;
        xSqSum += Math.pow(value.day, 2);
    });
    var slope = ((count * xySum) - (xSum * ySum)) / ((count * xSqSum) - Math.pow(ySum, 2));
    // Calculating the y-intercept (b) of the Trendline

    var yIntercept = (ySum - slope*xSum) / count;

    $.each(scores, function( index, value ) {
        value.trend = (value.day * slope) + yIntercept;
    });
};