async iteratros with buffer limit

chan.js

function chan(n) {
  let internalQueue = []
  let drain = null

  async function* wrappedIterator() {
    while (true) {
      if (internalQueue.length) {
        if (drain) drain()
        yield internalQueue.shift()
      }
    }
  }

  function write(data) {
    return new Promise((resolve, reject) => {
      if (internalQueue.length <= 5) {
        internalQueue.push(data)
        return resolve()
      }

      if (internalQueue.length >= 5) {
        drain = () => {
          internalQueue.push(data)
          drain = null
          resolve()
        }
      }
    })
  }

  return { values: wrappedIterator, write }
}

async function main() {
  let count = 0
  let c = chan(5)

  async function doWrite() {
    await c.write({ data: `ITEM-${count++}` })
    doWrite()
  }

  doWrite()

  process.stdin.resume()
  process.stdin.setRawMode(true)
  process.stdin.on('data', async x => {
    let val = await c.values().next()
    console.log(val)
  })
}

main()