reflection of an graph javascript

var p1 = board.create('point', [0.0, 4.0]);
var p2 = board.create('point', [6.0, 1.0]);
var l1 = board.create('line', [p1, p2]);
var p3 = board.create('point', [3.0, 3.0]);

var rp1 = board.create('reflection', [p3, l1]);