I'm not using Express, but I'm trying extract POST data then to send a json as response, with no luck

I'm still very new to node.js so please bear with me.

I'm trying to extract POST data then sent a json as response, but I don't seem to be able to extract the data from the POST request and even worse I can't find the syntax for people who are NOT using Express to send the json. It keeps telling me res.json is not a function.

server = http.createServer(function (req, res) {
    try {
        var body = "";
        var post = qs.parse("");
        if (req.method == "POST") {
        res.writeHeader(200, {"Content-Type": "application/json"});
        req.on("data", function (data) {
        body += data;
        console.log(data); //It gives something like <Buffer xx xx xx ...>
        if (body.length > 1e6)
            req.connection.destroy();
        });
    req.on("end", function () {
        post = qs.parse(body);
        console.log(post.test); //It gives "undefined"
    });
    res.json({ a: 1 });
    } catch(err) {
        console.dir(err);
        res.writeHeader(200, {"Content-Type": "text/plain"});
        res.end("Hello W3Cschool\n");
    }
});

server.listen(8000);
console.log("http start @8000");

Any help? Thanks in advance.

via Jenny L.