The Cookboox provides some examples of simple scripts that can help you get started. Feel free to take them and modify them for use in your own campaigns.

Reactive Script Examples

Bloodied and Dead Status Markers (Contributed by Ken Bauer)

This script automatically adds the Red marker to represent the "bloodied" state for any tokens that drop below half their health, and the "dead" market for any that drop to 0 or less. It's assumed that health is stored in Bar 1.

on("change:graphic", function(obj) {
    if(obj.get("bar1_max") === "") return;
   
    if(obj.get("bar1_value") <= obj.get("bar1_max") / 2) {
        obj.set({
              status_redmarker: true
        });
    }
    else{
        obj.set({
            status_redmarker: false
        })
    }

    if(obj.get("bar1_value") <= 0) {
      obj.set({
         status_dead: true
      });
    }
    else {
      obj.set({
        status_dead: false
      });
    }
});

The Darkness is Closing In...

This script reduces the light radius of a token by 10% every time that token moves. Great for simulating "lamps running out of oil" or similar high-stress situations.

on("change:token", function(obj) {
    //Only do this if we actually moved.
    if(obj.get("left") == obj.previous("left") && obj.get("top") == obj.previous("top")) return;
    obj.set({
        light_radius: Math.floor(obj.get("light_radius") * 0.90)
    });
});

Proactive Script Examples