So the idea is to create A plane at z = 0 and infinite x y.
then make A ray from the mouse position and find where it intersects.
I'm not sure how to create that plane and I don't know if the is the best way.
also this is a 2d scene and everything is on the z = 0
var projector = new THREE.Projector();
var mouse_vector = new THREE.Vector3();
var mouse = { x: 0, y: 0, z: 1 };
ray = new THREE.Raycaster( new THREE.Vector3(0,0,0), new THREE.Vector3(0,0,0) ),
var intersects = [];
event_info.preventDefault();
mouse.x = ( event_info.clientX / window.innerWidth ) * 2 – 1;
mouse.y = – ( event_info.clientY / window.innerHeight ) * 2 + 1;
mouse_vector.set( mouse.x, mouse.y, mouse.z );
projector.unprojectVector( mouse_vector, camera );
var direction = mouse_vector.sub( camera.position ).normalize();
ray = ray.set( camera.position, direction );
var plane = new THREE.Plane();
plane.set(v1, v2, v3);
var where = ray.intersectPlane (plane);
intersects = ray.intersectPlane( Plane );
alert(intersects);
}