Create a promise with a guard and an external resolver for performing some tasks before resolving

createPromiseWithGuardAndExternalResolver.js

/**
 * Save some data
 */
const persistData = data => {
    // persist the data
};

/**
 * Fetch some data, persist it and resolve a promise by given resolve function.
 *
 * @param {function} resolve - Some resolve from some Promise
 * @return {Promise}         - A promise from the fetch api
 */
const fetchAndPersistAndResolve = resolve =>
    fetch('url')
    .then(data => {
        persistData(data.json());
        resolve();
    });

/**
 * This function is passed below to the promise creator, so it becomes the promise's guard
 *
 * @return {boolean}
 */
const checkSomething = () => true;

/**
 * Create a promise which uses a given guard and a given external resolver
 *
 * @param {function} guard            - A guard that returns a boolean, false if the promise needs to be rejected
 * @param {function} externalResolver - An external function, performs other tasks before resolving the promise
 */
const createPromiseWithGuardAndExternalResolver = (guard, externalResolver) =>
    new Promise((resolve, reject) => {
        if (!guard()) {
            reject();
            // TODO: not sure, if this return statement is necessary
            return;
        }

        externalResolver(resolve)
            .catch(reject);
    });

const p = createPromiseWithGuardAndExternalResolver(checkSomething, fetchAndPersistAndResolve);