Reducers

Reducers are responsible for turning (currentState, action) into nextState.

In HexaJS, reducer classes use decorators:

• @Reducer() on the class.
• @Reduce(ACTION_TYPE) on each handler method.

Reducer example

import { HexaReducer, Reduce, Reducer } from '@hexajs-dev/core';
import * as BackgroundActions from './background.actions';

@Reducer()
export class LastContentCallReducer extends HexaReducer<LastContentCallState> {
  initialState: LastContentCallState = {
    message: '',
    timestamp: 0,
  };

  @Reduce(BackgroundActions.CONTENT_CALLED)
  onContentCalled(
    state: LastContentCallState,
    action: ReturnType<typeof BackgroundActions.contentCalled>
  ): LastContentCallState {
    if (!action.payload?.message || !action.payload?.timestamp) {
      return state;
    }
    return { ...action.payload };
  }
}

Reducer rules

• Return a new object when state changes.
• Return state unchanged when payload is invalid or action is not applicable.
• Keep reducer methods deterministic and side-effect free.
• Perform logging/IO in services/controllers/handlers, not reducers.

CLI and compiler behavior

• Use hexa generate reducer <name> <context> to scaffold reducer classes.
• Use hexa generate state <name> <context> to register reducer slices under @State(...).
• The CLI scanner (packages/cli/src/compiler/store/reducer/scanner.ts) discovers reducer metadata during build.

Where reducers are used

Reducers power both:

• Background store transitions driven by controllers/actions.
• Content store transitions driven by handlers/actions.