Express js: How to download a file using POST request

When I use GET, everything works fine. However, I struggle to use POST to achieve the same effect. Here are the code I have tried:

1.

app.post("/download", function (req, res) {
    res.download("./path");
});

2.

app.post("/download", function (req, res) {
    res.attachment("./path");
    res.send("ok");
});

3.

app.post("/download", function (req, res) {
    res.sendFile("./path");
});

None of them work. What is the correct way to do this?

EDIT: I submit a POST request through a HTML form to /download. ./path is a static file. When I use code in method 1, I can see the correct response header and response body in the developer tool. But the browser does not prompt a download.