stream-concat.js

var Transform = require('stream').Transform;

class StreamConcat extends Transform {
    constructor(streams, options) {
        super(options);
        this.streams = streams;
        this.canAddStream = true;
        this.currentStream = null;
        this.streamIndex = 0;

        this.nextStream();
    }
    
    nextStream () {
        this.currentStream = null;
        if (Array.isArray(this.streams) && this.streamIndex < this.streams.length) {
            this.currentStream = this.streams[this.streamIndex++];
        } else if (typeof this.streams === 'function') {
            this.canAddStream = false;
            this.currentStream = self.streams();
        }

        if (this.currentStream === null) {
            this.canAddStream = false;
            this.push(null);
        } else {
            this.currentStream.pipe(this, {end: false});
            this.currentStream.on('end', () => this.nextStream());
        }
    }


    addStream (newStream) {
        if (this.canAddStream)
            this.streams.push(newStream);
        else
            this.emit('error', new Error('Can\'t add stream.'));
    }

    _transform (chunk, encoding, callback) {
        callback(null, chunk);
    }
};