buffered-async-iterator

buffer wraps an async iterator into another async iterator, buffering items from the wrapped async iterator. This buffering allows the inner iterator to produce items concurrently with consumption of the items from the outer iterator. An example will help:

const buffer = require('buffered-async-iterator');

const someSlowIterator = ..;

for await (let item of buffer(someSlowIterator, 20)) {
  await someSlowOperation(item);
}

Here, someSlowIterator can slowly produce items (perhaps it is querying them from a database) and we can perform someSlowOperation on those items (perhaps calling some HTTP API). Both the DB queries and the HTTP calls will happen concurrently.

Without this functionality (that is, with for await (let item of someSlowIterator)), the DB queries and the HTTP calls would alternate, each unnecessarily waiting for the other.

The buffer has a length property which gives the current number of buffered items.

const buf = buffer(someSlowIterator, 20);
for await (let item of buffer) {
  await someSlowOperation(item);
  console.log(`${buf.length} items currently buffered`);
}

Inspiration

Inspired by https://github.com/mirkokiefer/async-iterators but updated for modern async iterators