api.js

import { Schema, arrayOf, normalize } from 'normalizr';
import { camelizeKeys } from 'humps';
import axios from 'axios';

const API_ROOT = 'http://localhost:5555/api/v1/';

// Fetches an API response.
// This makes every API response have the same shape, regardless of how nested it was.
function callApi(endpoint, method = 'get', data = {}, schema = null) {
  const fullUrl = (endpoint.indexOf(API_ROOT) === -1) ? API_ROOT + endpoint : endpoint;

  if (method.toLowerCase() == 'get') {
    return axios.get(
      fullUrl,
      { params: data }
    );
  }
  else {
    return axios.post(
      fullUrl,
      data
    );
  }
}

// Action key that carries API call info interpreted by this Redux middleware.
export const CALL_API = Symbol('Call API');

// A Redux middleware that interprets actions with CALL_API info specified.
// Performs the call and promises when such actions are dispatched.
export default store => next => action => {
  const callAPI = action[CALL_API];
  if (typeof callAPI === 'undefined') {
    return next(action);
  }

  let { endpoint } = callAPI;
  const { schema, types, method, data } = callAPI;

  if (typeof endpoint === 'function') {
    endpoint = endpoint(store.getState());
  }

  if (typeof endpoint !== 'string') {
    throw new Error('Specify a string endpoint URL.');
  }
  if (!Array.isArray(types) || types.length !== 3) {
    throw new Error('Expected an array of three action types.');
  }
  if (!types.every(type => typeof type === 'string')) {
    throw new Error('Expected action types to be strings.');
  }

  function actionWith(data) {
    const finalAction = Object.assign({}, action, data);
    delete finalAction[CALL_API];
    return finalAction;
  }

  const [requestType, successType, failureType] = types;
  next(actionWith({ type: requestType }));

  return callApi(endpoint, method, data, schema).then(
    response => next(actionWith({
      response,
      type: successType
    })),
    error => next(actionWith({
      type: failureType,
      error: error.message || 'Something went wrong!'
    }))
  );
};