How to post to a request using node.js

The issue is that you are setting Content-Type in the wrong place. It is part of the request headers, which have their own key in the options object, the first parameter of the request() method. Here’s an implementation using ClientRequest() for a one-time transaction (you can keep createClient() if you need to make multiple connections to the same server):

var http = require('http')

var body = JSON.stringify({
    foo: "bar"
})

var request = new http.ClientRequest({
    hostname: "SERVER_NAME",
    port: 80,
    path: "/get_stuff",
    method: "POST",
    headers: {
        "Content-Type": "application/json",
        "Content-Length": Buffer.byteLength(body)
    }
})

request.end(body)

The rest of the code in the question is correct (request.on() and below).