Post request in an iframe with express.js

I am using nodejs and the framework express.js to realize my website.

I am submitting a POST request on an url (/report/reportname) reportname is a variable.

so I do this :

app.post('/report/:id', function(req, res){ 
res.send("test");
}

and in my index.html I do : ( ID= a variable )

<form action='/report/ID' method='POST' target='FOO'></form>

<iframe name='FOO'></iframe>

When i click on submit it redirect me on the page /report/ID and i see the word : test and the iframe is not refreshed.

How can I do ? ( And I have to use res.send(something); )

Thanks !