where do .on(), .write(), pipe() and other nodejs method originate from?

I'm learning nodeJS and I was looking at code regarding streaming data from text. More specifically how to write to streams and piping to a writable stream (if I'm saying that correct). These are the two pieces of code are as follows:

var fs = require('fs');

var readable = fs.createReadStream(__dirname + '/greet.txt', { encoding: 'utf8', highWaterMark: 16 * 1024 });

var writable = fs.createWriteStream(__dirname + '/greetcopy.txt');

readable.on('data', function(chunk) {
    console.log(chunk);
    writable.write(chunk);
});

var fs = require('fs');
var zlib = require('zlib');

var readable = fs.createReadStream(__dirname + '/greet.txt');

var writable = fs.createWriteStream(__dirname + '/greetcopy.txt');

var compressed = fs.createWriteStream(__dirname + '/greet.txt.gz');

var gzip = zlib.createGzip();

readable.pipe(writable);

readable.pipe(gzip).pipe(compressed);

This is a noob question but are the .on(), .write() and .pipe() methods built into Nodejs itself (so it applies to all variables) or is it somehow added on when the variables writable/readable are assigned the functions in the fs module? I'm guessing this applies to other methods I will come across while learning.

via DanT29