nodejs this property and destroy() method

I am learning Nodejs with node cookbook 2nd edition.

I like this book because it is teaching us with explaining sample code which looks very practical.

Anyway the main question is that below is in the EX code

var http = require('http');
//We are synchronously loading form.htmlat initialization time instead of accessing the disk on each request. 
var form = require('fs').readFileSync('form.html');

var maxData = 2 * 1024 * 1024; //2mb


var querystring = require('querystring');
var util = require('util');

http.createServer(function (request, response) {
    if(request.hasOwnProperty('destroy')){console.log('!!!!!!')};
    if (request.method === "GET") {
        response.writeHead(200, {'Content-Type': 'text/html'});
        response.end(form);
    }

    if (request.method === "POST") {
        var postData = '';
        request.on('data', function (chunk) {
            postData += chunk;  
            if (postData.length > maxData) {
                postData = '';
                // this?? stream.destroy();
                this.destroy();
                response.writeHead(413); // Request Entity Too Large
                response.end('Too large');
            }
        }).on('end', function() {
            if (!postData) { response.end(); return; } // prevents empty post which requests from, crash
            var postDataObject = querystring.parse(postData);
            console.log('User Posted:\n' + postData);
            //inspect :  for a simple way to output our postDataObjectto the browser.
            response.end('You Posted:\n' + util.inspect(postDataObject));
        });
    }

}).listen(8080);

: This is HTTP server dealing with basic 'post' request from web user

over there, I do not figure out what is ( this.destroy(); ).

I guess that this is request readable streaming object. is not it? And I can understand what destroy() object is doing ( preventing any further data arriving from the client) but I cannot find destroy method at NodeJS API reference. (http://nodejs.org/api/all.html)

Can you explain me what is the this object and where is the destroy() method from?