how to parse json after exception handling promise with isomorphic-fetch

Question

During implementing login feature with React, Redux, isomorphic-fetch, ES6 Babel.

Questions

I do not know how to properly combine promises after the checkstatus promise in order to get parsed JSON data from my server.
what am I doing wrong here?

also, do I need to replace isomorphic-fetch package with other more convenient one?
any suggestion for other package is welcome!

loginAction.js

import * as API from '../middleware/api';
import * as ActionTypes from '../actionTypes/authActionTypes';
import 'isomorphic-fetch';

function encodeCredentials(id, pwd) {
  return btoa(`${id}{GS}${pwd}`);
}

function checkStatus(response) {
  if (response.status >= 200 && response.status < 300) {
    response;
  } else {
    const error = new Error(response.statusText);
    error.response = response;
    throw error;
  }
}

function parseJSON(response) {
  return response.json();
}

export function loginFailure(error) {
  return { error, type: ActionTypes.LOGIN_FAILURE };
}

export function loginSuccess(response) {
  return dispatch => {
    dispatch({ response, type: ActionTypes.LOGIN_SUCCESS });
  };
}

export function loginRequest(id, pwd) {
  return {
    type: ActionTypes.LOGIN_REQUEST,
    command: 'login',
    lang: 'en',
    str: encodeCredentials(id, pwd),
    ip: '',
    device_id: '',
    install_ver: '',
  };
}


export function login(id, pwd) {
  const credentials = loginRequest(id, pwd);

  return dispatch => {
    fetch(`${API.ROOT_PATH}${API.END_POINT.LOGIN}`, {
      method: 'post',
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(credentials),
    })
    .then(checkStatus)
    .then(parseJSON)
    .then(data => {
      console.log(`parsed data ${data}`);
      dispatch(loginSuccess(data));
    })
    .catch(error => {
      console.log(`request failed ${error}`);
    });
  };

}

Answer 1

In my projects usually, I have a helper function fetchJSON that does all utility logic, such as JSON parsing and status check.

Here it is:

import fetch from 'isomorphic-fetch';

function checkStatus(response) {
  if(response.ok) {
    return response;
  } else {
    const error = new Error(response.statusText);
    error.response = response;
    throw error;
  }
}

function parseJSON(response) {
  return response.json();
}

export default function enhancedFetch(url, options) {
  options.headers = Object.assign({
    'Accept': 'application/json',
    'Content-Type': 'application/json'
  }, options.headers);
  if(typeof options.body !== 'string') {
    options.body = JSON.stringify(options.body);
  }
  return fetch(url, options)
    .then(checkStatus)
    .then(parseJSON);
}

Then you can use it in actions:

import fetchJSON from '../utils/fetchJSON'; // this is the enhanced method from utilities

export function login(id, pwd) {
    const credentials = loginRequest(id, pwd);

    return dispatch => {
       fetchJSON(`${API.ROOT_PATH}${API.END_POINT.LOGIN}`, {
           method: 'post',
           body: credentials
       }).then(data => {
           console.log(`parsed data ${data}`);
           dispatch(loginSuccess(data));
       }).catch(error => {
           console.log(`request failed ${error}`);
       });
   };
}

It helps you to keep actions code clean from some boilerplate code. In big projects with tons of similar fetch calls it is a really must-have thing.

Answer 2

You're doing it right, you just forgot return in checkstatus; you should return the response such that the next promise in the chain can consume it.

Also, it seems that checkstatus is synchronous operation, so it's no need to chain it by .then (although, it's OK if you like it that way), you can write:

fetch(...)
.then(response=>{
   checkStatus(response)
   return response.json()
})
.then(data=>{
   dispatch(loginSuccess(data))
})
.catch(...)

I see no reason to get rid of isomorphic-fetch for now - it seems that it does its job.