Button-Callback from string

[cheshirepuss42]

I'm trying to make a game which is basically a grid where the player moves across. When the player moves on certain squares the first panel of a dialog tree will be presented: Some text, an image and some choices. The dialog trees I want to be able to make in JSON.
For the choices there is a text and an action to be taken on that choice. I made the choices using Phaser.button, which has callback:Function as a parameter. Things I want to be able to do are fx. modify player health, spawn enemy, modify energy, so all kinds of stuff.
I don't really have a clue how to do this in phaser. I understand that i need some reference to the gamedata, but how to run a method like game.player.modifyhealth(-10) from something like this {callback:"game.player.modifyhealth",mod:-10} when i press a certain button? So what do i pass to Phaser.button as callback?

[cheshirepuss42]

Does anybody have any idea? I know it might not be Phaser-specific, but it does seem something that a lot of games use. Maybe I'm just barking up the wrong tree, and the way to do this is completely different from how I'm approaching it. But I would love to know this.