node.js writable buffer stream (pdfkit example)

example.js

/**
 * Convert PDFDocument to Base64
 */
const PDFDocument = require('pdfkit');
const stream = require('./stream');

// crate document and write stream
let doc = new PDFDocument();
let writeStream = new stream.WritableBufferStream();

// pip the document to write stream
doc.pipe(writeStream);

// add some content
doc.text('Some text!', 100, 100);

// end document
doc.end()

// wait for the writing to finish
writeStream.on('finish', () => {
  // console log pdf as bas64 string
  console.log(writeStream.toBuffer().toString('base64'));
});

stream.js

const stream = require('stream');

/**
 * Simple writable buffer stream
 * @docs: https://nodejs.org/api/stream.html#stream_writable_streams
 */
class WritableBufferStream extends stream.Writable {

    constructor(options) {
        super(options);
        this._chunks = [];
    }

    _write (chunk, enc, callback) {
        this._chunks.push(chunk);
        return callback(null);
    }

    _destroy(err, callback) {
        this._chunks = null;
        return callback(null);
    }

    toBuffer() {
        return Buffer.concat(this._chunks);
    }
}

module.exports = { WritableBufferStream }

Thx for the feedback, added the export.