Migrate command emit to effects

Ignite Element now treats commands as intent triggers and effects as the place where state transitions produce DOM events.

Before

const registerToggle = igniteCore({
  source: machine,
  events: (event) => ({
    toggled: event<{ isOn: boolean }>(),
  }),
  commands: ({ actor, emit }) => ({
    toggle: () => {
      actor.send({ type: "TOGGLE" });
      emit("toggled", { isOn: true });
    },
  }),
});

After

const registerToggle = igniteCore({
  source: machine,
  events: (event) => ({
    toggled: event<{ isOn: boolean }>(),
  }),
  commands: ({ actor }) => ({
    toggle: () => {
      actor.send({ type: "TOGGLE" });
    },
  }),
  effects: ({ snapshot, prevSnapshot, emit }) => {
    if (snapshot.matches("on") === prevSnapshot.matches("on")) return;
    emit("toggled", { isOn: snapshot.matches("on") });
  },
});

Migration checklist

1. Remove emit from the commands parameter list.
2. Keep commands limited to actor/store/observable intent.
3. Add effects(snapshot, prevSnapshot, ctx).
4. Compare snapshot with prevSnapshot before emitting.
5. Keep your events map so emit stays typed.

Scripted assist

From the repo root:

node scripts/migrate-emit-to-effects.mjs

The script reports files that still:

• destructure emit in commands
• call emit(...) in code that likely needs migration

Use --report <path> to save the output to a file.

Breaking release note

emit has been removed from command context. Commands still receive { actor, command, host }; typed event emission belongs in effects().

Release boundary

• Migration tooling and docs remain available to help with old command emit patterns.
• effects() is now the supported path for typed event emission.