Callbacks and state

Oxidizer calls functions your script defines. All of them are optional.

Function	When
init()	Once, when the mod starts: before the game's Main, so before the game has loaded anything.
loaded()	Once, when the game has loaded its content and mods (Oxidizer 0.8 and later). Set up what needs the game's data here. No flight exists yet: the controlled vehicle comes later. A mod that starts after this point gets loaded() right after init().
frame(t, dt)	Every frame. t is the game's player time, dt the seconds since the last frame.
gui(dt)	Every frame, inside the game's ImGui frame: draw your windows here (see Windows and menus).
menu()	While the game's Mods menu is open: add your entries here.
reload()	After you saved the file and it was reloaded.
unload()	When the game closes.

Code at the top level of the file (outside functions) runs every time the file is loaded, before init or reload.

Keeping state in this

Variables declared with let inside a function are gone when it returns. For state that lasts, use this, an object map that belongs to your mod:

fn init() {
    this.frames = 0;
    this.visible = true;
}

fn frame(t, dt) {
    this.frames += 1;
}

fn gui(dt) {
    if !this.visible { return; }
    if begin("Counter") {
        text(`frames: ${this.frames}`);
    }
    end();
}

this survives hot reloads: when you save the file, the new code runs with the same this, and init() doesn't run again (reload() does). So you can change how a window looks while the mod keeps counting. To start over, restart the game, or reset values in reload().

Errors

A script that doesn't compile when the game starts doesn't run; fix the file and save, and it starts. When a function stops with an error while running, the mod stops until you save the file again, so an error in frame or gui isn't repeated every frame. Mods > Oxidizer shows the error with its line; in Rhai Studio it is above the editor.

print(...) writes to Oxidizer's log, which you see in Mods > Oxidizer.