Configurable fetch middleware implementation

fetch.middleware.js

import buildAsyncStages from "../stages/async-stages";
import { handleFetchError } from "../errors";

const ASYNC_FETCH = "ASYNC_FETCH";

const baseRequestOptions = { credentials: "same-origin" };

const fetchMiddleware = fetchImplementation => store => next => action => {
    next(action);

    if (action.type !== ASYNC_FETCH) return;

    const responseDescription = action.response || {};
    const customMappings = responseDescription.mappings || {};
    const mappings = {
        failure: res => ({ error: res && res.message }),
        ...customMappings
    };
    const stageBuilderArgs = [action.id, action.args, mappings];
    const stages = buildAsyncStages(...stageBuilderArgs)(store.dispatch);

    const requestDescription = action.request;
    const fetchRequest = new Request(requestDescription.url, {
        ...baseRequestOptions,
        ...requestDescription.options
    });

    stages.begin();

    return fetchImplementation(fetchRequest)
        .then(handleFetchError)
        .then(res => res.json())
        .then(res => stages.success(res))
        .catch(error => stages.failure(error));
};

export { ASYNC_FETCH };
export default fetchMiddleware;