function getAngle(line) {

  // return value is between 0, 180 and -180, -0
  // @janstuemmel: maybe replace return a/b with b/a
  return Math.atan((line[1].y - line[0].y) / (line[1].x - line[0].x));
}
Calculates the angle between a line a the Y axis.

@param {Point[]} line

@return {number}