This snippet makes sure that a layer is facing the camera. All tribute to Dan Ebberts - www.motionscript.com

normalToCamera.js

L = thisComp.layer("Camera 1"); 
u = fromWorldVec(L.toWorldVec([1,0,0])); 
v = fromWorldVec(L.toWorldVec([0,1,0])); 
w = normalize(fromWorldVec(L.toWorldVec([0,0,1]))); 

sinb = clamp(w[0],-1,1); 
b = Math.asin(sinb); 
cosb = Math.cos(b); 
if (Math.abs(cosb) > .0005){ 
  c = -Math.atan2(v[0],u[0]); 
  a = -Math.atan2(w[1],w[2]); 
}
else{
  a = (sinb < 0 ? -1 : 1)*Math.atan2(u[1],v[1]); 
  c = 0; 
} 
[radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)]