Batch transform stream javascript

batch_stream.js

const { Transform } = require('stream');


const batchStream = (batchSize = 5) => {
  let batch = [];

  return new Transform({
    objectMode: true,
    transform(data, _, done) {
      batch.push(data);

      if (batch.length >= batchSize) {
        done(null, batch);
        batch = [];
        return;
      }

      done();
    },
    flush(done) {
      done(null, batch);
    },
  });
};

// Call with .pipe(batchStream(20))
// In the next pipe, you will get an array of 20 (or the
// remainder in the last step) of "stuff" instead of one "stuff" at a time.
// loosely based on https://www.bennadel.com/blog/3236-using-transform-streams-to-manage-backpressure-for-asynchronous-tasks-in-node-js.htm