stream-concat.js

const { PassThrough } = require('stream');

function combineStream(...streams) {
    return streams.reduce((passthrough, stream, i) => {
        stream.pipe(passthrough);
        stream.once('end', () => {
            streams.every(s => s.ended);
            passthrough.emit('end');
        });
        return passthrough;
    }, new PassThrough());
}