Multiple clients posting data in node js

I've read that in Node js one should treat POST requests carefully because the post data may arrive in chunks, so it has to be handled like this, concatenating:

function handleRequest(request, response) {
    if (request.method == 'POST') {
        var body = '';
        request.on('data', function (data) {
            body += data;
        });
        request.on('end', function () {
            //data is complete here
        });
    }
}

What I don't understand is how this code snippet will handle several clients at the same time. Let's say two separate clients start uploading large POST data. They will be added to the same body, mixing up the data...

Or is it the framework which will handle this? Triggering different instances of handleRequest function so that they do not get mixed up in the body variable?

Thanks.