Convert a stream to Promise

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I need to collect all the data from the stream and resolve it as promise.

I created this stream:

class CollectToPromise extends Writable {
  constructor(options) {
    this._result = ""

    this.result = new Promise((resolve, reject) => {
      this.on('finish', resolve):w
      this.on('error', reject)
    }).then(() => this._result)


  _write(chunk, encoding, callback) {
    this._result += chunk

  _writev(chunks, callback) {
    chunks.forEach(c => {
      this._result += chunk

  asPromise() {
    return this.result

and I use it like this:

var r = fs.createReadStream('secrets');
const c = new CollectToPromise()
const encrypt = crypto.createCipher(algorithm, password);
r.pipe(encrypt).pipe(c).asPromise().then((res) => console.log(res)

My questions are:

  1. What do you think about the solution, including the naming?
  2. How can I avoid the warning: (node:32386) Warning: Use Cipheriv for counter mode of aes-256-ctr?


I am not sure I understand why you are attempting to extend Writable here.

At the end of the day, it seems as if your pipeline is what you are REALLY wanting to have a promise interface.

Luckily this is really easy to do with recent versions of node using Stream.pipeline and Util.promisify(). There is an even an example in the Stream.pipeline documentation

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