actions.js

export const simpleAction = () => {
  return {
    type: 'SIMPLE_ACTION'
  };
};

export const complexAction = (arg) => {
  return {
    type: 'COMPLEX_ACTION',
    arg
  };
};

reducers.js

export const reducer = (state, action) => {
  switch(action.type) {
    case SIMPLE_ACTION:
      return {
        ...state,
        simple: true
      };
    case COMPLEX_ACTION:
      let arg = action.arg;
      if (arg > 100) {
        return {
          ...state,
          argOver100: true
        };
      }
      if (arg > 1000) {
        return {
          ..state,
          argOver1000: true
        };
      }
      if (arg === 599) {
        return {
          ..state,
          price: arg
        };
      }
      return state;
    default:
      return state;
  }
};