Make server validation using redux-form and Fetch API

Question

How to make server-side validation using redux-form and Fetch API? There are "Submit Validation" demo provided in the docs which says that recommended way to do server side validation is to return a promise from the onSubmit function. But where should I place that promise? As I understood onSubmit function should be my action.

<form onSubmit={this.props.addWidget}>...

Where this.props.addWidget is actually my action, provided below.

import fetch from 'isomorphic-fetch';
...
function fetchAddWidget(widget, workspace) {
    return dispatch => {
        dispatch(requestAddWidget(widget, workspace));
        return fetch.post(`/service/workspace/${workspace}/widget`, widget)
            .then(parseJSON)
            .then(json => {
                dispatch(successAddWidget(json, workspace));
                DataManager.handleSubscribes(json);
            })
            .catch(error => popupErrorMessages(error));
    }
}

export function addWidget(data, workspace) {
    return (dispatch, getState) => {
        return dispatch(fetchAddWidget(data, workspace));
    }
}

As you see I use fetch API. I expected that fetch will return promise and redux-form will catch it but that doesn't work. How to make it work with promise from example?

Also from the demo I can not understand what should be provided in this.props.handleSubmit function. Demo does not explain this part, as for me.

Answer 1

Here's my take on using fetch based on the example at http://erikras.github.io/redux-form/#/examples/submit-validation.

• ...but where should I place that promise?
• ...what should be provided in this.props.handleSubmit?

The detail is in the comments below; sorry that the code blocks require a bit of scrolling to read :/

---

components/submitValidation.js

import React, { Component, PropTypes } from 'react';
import { reduxForm } from 'redux-form';
import { myHandleSubmit, show as showResults } from '../redux/modules/submission';

class SubmitValidationForm extends Component {
  // the following three props are all provided by the reduxForm() wrapper / decorator
  static propTypes = {
    // the field names we passed in the wrapper;
    // each field is now an object with properties:
    // value, error, touched, dirty, etc
    // and methods onFocus, onBlur, etc
    fields: PropTypes.object.isRequired,

    // handleSubmit is _how_ to handle submission:
    // eg, preventDefault, validate, etc
    // not _what_ constitutes or follows success or fail.. that's up to us

    // I must pass a submit function to this form, but I can either:

    // a) import or define a function in this component (see above), then: 
    //   `<form onSubmit={ this.props.handleSubmit(myHandleSubmit) }>`, or

    // b) pass that function to this component as 
    //   `<SubmitValidationForm onSubmit={ myHandleSubmit } etc />`, then 
    //   `<form onSubmit={this.props.handleSubmit}>`
    handleSubmit: PropTypes.func.isRequired,

    // redux-form listens for `reject({_error: 'my error'})`, we receive `this.props.error`
    error: PropTypes.string
  };

  render() {
    const { fields: { username, password }, error, handleSubmit } = this.props;

    return (
      <form onSubmit={ handleSubmit(myHandleSubmit) }>

        <input type="text" {...username} />
        {
            // this can be read as "if touched and error, then render div"
            username.touched && username.error && <div className="form-error">{ username.error }</div>
        }

        <input type="password" {...password} />
        { password.touched && password.error && <div className="form-error">{ password.error }</div> }

        {
          // this is the generic error, passed through as { _error: 'something wrong' }
          error && <div className="text-center text-danger">{ error }</div>
        }

        // not sure why in the example @erikras uses 
        // `onClick={ handleSubmit }` here.. I suspect a typo.
        // because I'm using `type="submit"` this button will trigger onSubmit
        <button type="submit">Log In</button>
      </form>
    );
  }
}

// this is the Higher Order Component I've been referring to 
// as the wrapper, and it may also be written as a @decorator
export default reduxForm({
  form: 'submitValidation',
  fields: ['username', 'password'] // we send only field names here
})(SubmitValidationForm);

---

../redux/modules/submission.js

// (assume appropriate imports)

function postToApi(values) {
  return fetch( API_ENDPOINT, {
    credentials: 'include',
    mode: 'cors',
    method: 'post',
    body: JSON.stringify({values}),
    headers: {
      'Content-Type': 'application/json',
      'X-CSRFToken': CSRF_TOKEN
    }
  }).then( response => Promise.all([ response, response.json()] ));
}

export const myHandleSubmit = (values, dispatch) => {
  dispatch(startLoading());

  return new Promise((resolve, reject) => {
    // postToApi is a wrapper around fetch
    postToApi(values)
      .then(([ response, json ]) => {
        dispatch(stopLoading());

        // your statuses may be different, I only care about 202 and 400
        if (response.status === 202) {
          dispatch(showResults(values));
          resolve();
        }
        else if (response.status === 400) {
          // here I expect that the server will return the shape:
          // {
          //   username: 'User does not exist',
          //   password: 'Wrong password',
          //   _error: 'Login failed!'
          // }
          reject(json.errors);
        }
        else {
          // we're not sure what happened, but handle it:
          // our Error will get passed straight to `.catch()`
          throw(new Error('Something went horribly wrong!'));
        }
      })
      .catch( error => {
        // Otherwise unhandled server error
        dispatch(stopLoading());
        reject({ _error: error });
      });
  });
};

---

Please chime in with comments if I've missed something / misinterpreted, etc, and I'll amend :)

Answer 2

It turned out that there are undocumented property returnRejectedSubmitPromise which must be set to true.