redux-middleware-example.js

export const validation = store => next => action => {
  switch(action.type){
    case loginFormSubmit.type: {
      const isValid = validate(action.payload);
      if (isValid) return next(action)
      // else
      store.dispatch(loginFormIvalid())
    }
    default: return next(action)
  }
};

// ...
applyMiddleware(thunk, validation)