If you are going for easy, you can just have GET data in the URL. But, that doesn't look that nice, if you want a rather long message, plus, GET has size restrictions, where POST (virtually) hasn't.
For using post data you could use the solution of this: JavaScript post request like a form submit question, but that gives a rather messy source code (if you want a somewhat longer text).
You could keep them in a database, and only send the ID of the message to a PHP page, and get it from the database (that's what I would do, but that doesn't mean it's a good idea, just amateur here!)