How to cancel a redirect after receiving a response from the server?

Question

Node.js

after sending a response from the server

app.post("/upload",function (req, res, next) {
        if(!filedata)
            res.send("Ошибка при загрузке файла");
        else
        res.sendStatus(200)
    });

The client is redirected to another page, how to avoid this?