A wrapping factory object for node.js createReadStream to promisify the read stream. Handles adding and removing event listeners for GC.

ReadStreamFactory.ts

import { createReadStream, ReadStream } from 'fs'

class ReadStreamFactory {
  private readStream: ReadStream
  private promiseResolve: (stream: ReadStream) => void
  private promiseReject: (reason: Error) => void

  static createReadStream(filename: string): Promise<ReadStream> {
    const factory = new ReadStreamFactory(filename)
    return factory.promisifyReadStream()
  }

  private constructor(filename: string) {
    this.readStream = createReadStream(filename)
    this.onError = this.onError.bind(this)
    this.onReadable = this.onReadable.bind(this)
  }

  private promisifyReadStream(): Promise<ReadStream> {
    return new Promise((resolve, reject) => {
      this.promiseResolve = resolve
      this.promiseReject = reject
      this.addListeners()
    })
  }

  private addListeners() {
    this.readStream.addListener('error', this.onError)
    this.readStream.addListener('readable', this.onReadable)
  }

  private onError(e: Error) {
    this.promiseReject(e)
  }

  private onReadable() {
    this.removeListeners()
    this.promiseResolve(this.readStream)
  }

  private removeListeners() {
    this.readStream.removeListener('error', this.onError)
    this.readStream.removeListener('readable', this.onReadable)
  }
}

// Usage
(async () => {
  try {
    const stream: ReadStream = await ReadStreamFactory.createReadStream('filename.txt')
  } catch (e) {
    console.error(e.message)
  }
}())