If you want to calculate trendline datapoints in TypeScript, you can use the following code:

### Code

module helpers.math { 'use strict'; /** * Based off: https://github.com/Tom-Alexander/regression-js/blob/master/src/regression.js * @param known_y - Array of numbers representing the y-axis values, [1, 2, ...]. * @param known_x - Optional array of numbers representing the x-axis values, when not supplied this parameter will be [1,2,..."y-axis values total count"]. */ export function trend(known_y: Array<number>, known_x?: Array<number>): Array<number> { const ylength = known_y.length; // When "x-axis values" are not supplied, generate it as [1,2,..."y-axis values total count"]. if (!known_x) { known_x = []; for (let xcounter = 0; xcounter < ylength; xcounter++) { known_x.push(xcounter + 1); } } // The "data" should be in the format [[x[0], y[0]], [x[1], y[1]]], ...]. const data = []; for (let ycounter = 0; ycounter < ylength; ycounter++) { data.push([known_x[ycounter], known_y[ycounter]]); } let n = 0; const results = []; const sum = [0, 0, 0, 0, 0]; for (; n < data.length; n++) { if (data[n][1] != null) { sum[0] += data[n][0]; sum[1] += data[n][1]; sum[2] += data[n][0] * data[n][0]; sum[3] += data[n][0] * data[n][1]; sum[4] += data[n][1] * data[n][1]; } } const gradient = (n * sum[3] - sum[0] * sum[1]) / (n * sum[2] - sum[0] * sum[0]); const intercept = (sum[1] / n) - (gradient * sum[0]) / n; for (let i = 0, len = data.length; i < len; i++) { const trendY = data[i][0] * gradient + intercept; results.push(trendY); } return results; } }

### Unit Test

const trend = helpers.math.trend; 'use strict'; describe('zvdz.helpers.calculate.trend', function () { it('given an array of points it should return an array of points representing the trendline of the given points.', function () { const known_y = [1,2,3,4,5,6]; expect(trend(known_y)).toEqual([1, 2, 3, 4, 5, 6]); }); });