add-stream

var fs = require('fs');
var es = require('event-stream');
var addStream = require('add-stream');
 
// Append strings/buffers
fs.createReadStream('1.txt') // 1.txt contains: number1
    .pipe(addStream(fs.createReadStream('2.txt'))) // 2.txt contains: number2
    .pipe(fs.createWriteStream('appended.txt')); // appended.txt contains: number1number2
 
// Append object streams
es.readArray([1, 2, 3])
    .pipe(addStream.obj(es.readArray([4, 5, 6])))
    .pipe(es.writeArray(function (err, array) {
        console.log(array); // [ 1, 2, 3, 4, 5, 6 ]
    }));