stream

const stream = require('stream');

Readable

class Readable()

const stream = new stream.Readable();
const data = ['1', '2', '3'];

stream._read = function(){
    if (data.length){
        setTimeout(function(){
            stream.push(data.shift());
        }, 200);
    } else {
        stream.push(null);
    }
};

stream.pipe(process.stdout);

Transform

class Transform()

const tr = new stream.Transform();

tr._transform = function(chunk, enc, cb){
    var string = String(chunk);
    this.push(string);
    cb();
};

process.stdin
    .pipe(tr)
    .pipe(process.stdout);