script effect

<script effect> is the opt-in source form for component-local Effect execution.

Source form

<script lang="ts" effect>
  import * as Effect from "effect/Effect";

  let count = $state(0);

  const increment = Effect.gen(function* () {
    count += 1;
  });
</script>

Transform semantics

• Declarations remain hoisted at component scope.
• Top-level executable statements are lowered into a mount-time Effect.gen(...).
• yield* declarations are preserved through the lowering pass.
• The generated program runs on mount.
• The generated program is canceled on unmount.
• HMR disposal is registered for running programs.