Help Teleporting to New Dimension

[lclc98]

I have been working on trying to check if a player is below y = 0 and teleport them to new dimension. Problem is that

if(player.posY == 0){}

returns null and have no clue how to fix it. Also i don't know how to teleport player to new world.

[Jdb100]

It should look like this.

if(player.posY <= 0){}