payloadValidation.js

var decrement = store.createChangeTrigger({
  actionType: 'DECREMENT',
  reducer: (state, payload, action) => {
    const value = payload.value || 1;
    return state - value;
  },

  // Payload validation - notice how it returns either reject() with a message or
  // accept() to let slim-redux know whether the validation passed or not.
  payloadValidation: (payload, accept, reject) => {
    if(!payload || !payload.value)
      return reject({
        msg: 'No parameters given or no "value" attribute in parameters provided!',
        params: payload
      });
    else
      return accept();
  }
});