How to send and receive variables with Javascript?

Yes, I've done this in a sample game that I'm working on. I've edited the code below to take out parts you don't need. This is in a trigger that's executed when the Storyline variable "NewMessage" changes. This inserts a line break between each new message entry.

var player = GetPlayer();
var oldDialog = player.GetVar("Dialog");
var newdialog = player.GetVar("NewMessage") + String.fromCharCode(13) + oldDialog;
player.SetVar("Dialog",newdialog);