how to return status: "ok" along with json data in nodejs code example

Example 1: node js return json

var http = require('http');

var app = http.createServer(function(req,res){
    res.setHeader('Content-Type', 'application/json');
    res.end(JSON.stringify({ a: 1 }));
});
app.listen(3000);

// > {"a":1}

Example 2: express set response code

res.status(400);
res.send('None shall pass');