code: function getAngle(p1, p2, props) {
    if (!props) {
      props = PROPS_XY;
    }
    var x = p2[props[0]] - p1[props[0]];
    var y = p2[props[1]] - p1[props[1]];
    return Math.atan2(y, x) * 180 / Math.PI;
  }
docs: calculate the angle between two coordinates
  @param {Object} p1
  @param {Object} p2
  @param {Array} [props] containing x and y keys
  @return {Number} angle