callbackhell.js

    app.post('/articles/:uuid/file', upload.array('file', 2), (req, res, next) => {
        const session = driver.session();

        let images = [];
        let captions = req.body.caption;

        const sessionUuid = uuidV4();

        req.files.forEach((file, index) => {
            images.push(Object.assign({}, {
                url: `uploads/articles/${req.params.uuid}/${file.originalname}`,
                caption: captions[index],
                name: file.originalname,
                sessionUuid,
            }))
        })

        const currentTimestamp = moment().format('YYYY-MM-DD HH:MM:SS');

        images.forEach((image, index) => {
            const tempSession = driver.session();

            let writeTxPromise = tempSession.writeTransaction(tx => {
                tx.run(`MATCH (n:Article {uuid: $uuid})
                                MERGE (n)-[:HAS]->(i:File {
                                    name: $name,
                                    caption: $caption
                                }) WITH i,n SET i.uuid = $fileUuid,
                                i.session_uuid = $sessionUuid,
                                i.url = $url,
                                i.updated_at = $updatedAt,
                                i.created_at = $createdAt RETURN n`,
                    {
                        uuid: req.params.uuid,
                        sessionUuid,
                        fileUuid: uuidV4(),
                        url: image.url,
                        name: image.name,
                        caption: image.caption,
                        createdAt: currentTimestamp,
                        updatedAt: currentTimestamp,
                    });
            });

            writeTxPromise.then(result => {
                console.log('File saved.');
                tempSession.close();

                const isLastImagePromise = (index + 1 === images.length);
                if (isLastImagePromise) {
                    session.readTransaction(tx => tx.run(
                        `MATCH a=(n:Article {uuid: $uuid})
                                WHERE SIZE((n)-[:HAS]->()) = 0
                                WITH COLLECT(a) AS bs CALL apoc.convert.toTree(bs) yield value RETURN value
                                UNION MATCH b=(n:Article)-[:HAS*]->(m) WITH COLLECT(b) AS as CALL apoc.convert.toTree(as) yield value RETURN value`,
                        {
                            uuid: req.params.uuid,
                        })).then(result => {
                        session.close();

                        const article = result.records[0]._fields[0];
                        const savedFiles = article.has || [];
                        const tooManyFiles = savedFiles.length > 2;

                        let responseFiles = savedFiles;

                        if (tooManyFiles) {
                            responseFiles = savedFiles.filter(file => file.session_uuid === sessionUuid);

                            savedFiles.forEach(file => {
                                if (file.session_uuid === sessionUuid) {
                                    return;
                                }
                                const cleanupSession = driver.session();
                                cleanupSession.writeTransaction(tx => tx.run(
                                    `MATCH (f:File {uuid: $uuid}) DETACH DELETE f`,
                                    {
                                        uuid: file.uuid
                                    }
                                )).then(result => {
                                    cleanupSession.close();
                                }).catch(error => console.log(error));
                            })
                        }

                        // on application exit:
                        driver.close();

                        let response = {
                            data: Object.assign({}, article, {
                                has: responseFiles
                            })
                        };

                        res.send(response);
                    });
                }
            }).catch(error => {
                console.log(error);
                driver.close();
            })
        })
    })