A gist that simplifies fetching data with Qt5.12 with a JavaScript flavor.

Fetcher.cpp

#include <QtNetwork/QNetworkReply>
#include <iostream>
#include "Fetcher.h"

void Fetcher::get(QString url, std::function<void(QNetworkReply *)> callback) {
    int id = m_id++;
    QNetworkReply *reply = m_nam.get(QNetworkRequest(QUrl(url)));
    m_replies.insert(id, reply);

    connect(reply, &QNetworkReply::finished, this, [&, id, callback]() {
        QNetworkReply *r = m_replies.take(id);

        callback(r);

        r->deleteLater();
    });
}

Fetcher.h

#include <QtNetwork/QNetworkAccessManager>
#include <QtCore/QHash>
#include <QtCore/QSignalMapper>

class Fetcher : public QObject {
    Q_OBJECT
    int m_id = 0;
    QNetworkAccessManager m_nam;
    QHash<int, QNetworkReply*> m_replies;
public:
    void get(QString url, std::function<void(QNetworkReply *)>);
};