accounts-frontend/src/services/request.js

function convertQueryValue(value) {
    if (typeof value === 'undefined') {
        return '';
    }

    if (value === true) {
        return 1;
    }

    if (value === false) {
        return 0;
    }

    return value;
}

function buildQuery(data = {}) {
    return Object.keys(data)
        .map(
            (keyName) =>
                [keyName, convertQueryValue(data[keyName])]
                    .map(encodeURIComponent)
                    .join('=')
        )
        .join('&')
        ;
}

const middlewares = [];

const checkStatus = (resp) => Promise[resp.status >= 200 && resp.status < 300 ? 'resolve' : 'reject'](resp);
const toJSON = (resp) => resp.json();
const rejectWithJSON = (resp) => toJSON(resp).then((resp) => {throw resp;});
const handleResponseSuccess = (resp) => Promise[resp.success || typeof resp.success === 'undefined' ? 'resolve' : 'reject'](resp);

function doFetch(url, options = {}) {
    // NOTE: we are wrapping fetch, because it is returning
    // Promise instance that can not be pollyfilled with Promise.prototype.finally

    options.headers = options.headers || {};
    options.headers.Accept = 'application/json';

    return runMiddlewares('before', {url, options})
        .then(({url, options}) => fetch(url, options))
        .then(checkStatus)
        .then(toJSON, rejectWithJSON)
        .then(handleResponseSuccess)
        .then((resp) => runMiddlewares('then', resp))
        .catch((resp) => runMiddlewares('catch', resp, () => doFetch(url, options)))
        ;
}

/**
 * @param  {string} action - the name of middleware's hook (before|then|catch)
 * @param  {Object} data - the initial data to pass through middlewares chain
 * @param  {Function} restart - a function to restart current request (for `catch` hook)
 *
 * @return {Promise}
 */
function runMiddlewares(action, data, restart) {
    return middlewares
        .filter((middleware) => middleware[action])
        .reduce(
            (promise, middleware) => promise.then((resp) => middleware[action](resp, restart)),
            Promise[action === 'catch' ? 'reject' : 'resolve'](data)
        );
}

export default {
    post(url, data) {
        return doFetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
            },
            body: buildQuery(data)
        });
    },

    get(url, data) {
        if (typeof data === 'object') {
            const separator = url.indexOf('?') === -1 ? '?' : '&';
            url += separator + buildQuery(data);
        }

        return doFetch(url);
    },

    buildQuery,

    addMiddleware(middleware) {
        if (!middlewares.find((mdware) => mdware === middleware)) {
            middlewares.push(middleware);
        }
    }
};