combineStream.js

class CombinedStream extends stream.PassThrough {

    constructor (...streams) {
        super()

        this._streams = streams
        this._transformStream = undefined

        this.on('pipe', this.onPipe)
    }

    onPipe (sourceStream) {
        sourceStream.unpipe(this)

        for (const stream of this._streams) {
            sourceStream = sourceStream.pipe(stream)
        }

        const eventTypes = [
            'data',
            'end',

            'close',
            'drain',
            'error',
            'finish',
            'pipe',
            'unpipe',
        ]

        for (const eventType of eventTypes) {
            sourceStream.on(eventType, (...args) => {
                this.emit(eventType, ...args)
            })
        }

        this._transformStream = sourceStream
    }

    pipe (destinationStream, options) {
        return this._transformStream.pipe(destinationStream, options)
    }

}