Allow static config for stream subclasses

[ORESoftware]

Right now I have this:

export class JSONParser extends stream.Transform {

  lastLineData = '';

  constructor() {
      super({objectMode: true});
  }

  _transform(chunk: any, encoding: string, cb: Function) {

    let data = String(chunk);
    if (this.lastLineData) {
      data = this.lastLineData + data;
    }

    let lines = data.split('\n');
    this.lastLineData = lines.splice(lines.length - 1, 1)[0];

    lines.forEach(l => {
      try {
        // l might be an empty string; ignore if so
        l && this.push(JSON.parse(l));
      }
      catch (err) {
        // noop
      }
    });

    cb();

  }

  _flush(cb: Function) {
    if (this.lastLineData) {
      try {
        this.push(JSON.parse(this.lastLineData));
      }
      catch (err) {
        // noop
      }
    }
    this.lastLineData = '';
    cb();
  }

}

that seems to work, but what would be nice is something like this:

export class JSONParser extends stream.Transform {

  lastLineData = '';
  static options = {objectMode: true};   // <<< options are same for all instances

  constructor() {
    super();
  }

  _transform(chunk: any, encoding: string, cb: Function) {

    let data = String(chunk);
    if (this.lastLineData) {
      data = this.lastLineData + data;
    }

    let lines = data.split('\n');
    this.lastLineData = lines.splice(lines.length - 1, 1)[0];

    lines.forEach(l => {
      try {
        // l might be an empty string; ignore if so
        l && this.push(JSON.parse(l));
      }
      catch (err) {
        // noop
      }
    });

    cb();

  }

  _flush(cb: Function) {
    if (this.lastLineData) {
      try {
        this.push(JSON.parse(this.lastLineData));
      }
      catch (err) {
        // noop
      }
    }
    this.lastLineData = '';
    cb();
  }

}

it could potentially be more performant, but not that sure if it's worth it.

[apapirovski]

Given the lack of input from others and the fact that this is quite awkward to make work ergonomically, I don't think this is something that will actually get implemented in Node.js. That said, if you do want to see something like this the best way is to just do it yourself and open a PR — see where that goes. :) Do feel free to reopen if you feel strongly about this though.