Promise Pool

Map-like, concurrent promise processing for Node.js.

Installation · Docs · Usage

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Installation

npm i @supercharge/promise-pool

Docs

Find all the details and available methods in the extensive Supercharge docs.

Usage

Using the promise pool is pretty straightforward. The package exposes a class and you can create a promise pool instance using the fluent interface.

Here’s an example using a concurrency of 2:

const PromisePool = require('@supercharge/promise-pool')

const users = [
  { name: 'Marcus' },
  { name: 'Norman' },
  { name: 'Christian' }
]

const { results, errors } = await PromisePool
  .withConcurrency(2)
  .for(users)
  .process(async data => {
    const user = await User.createIfNotExisting(data)

    return user
  })

The promise pool uses a default concurrency of 10:

await PromisePool
  .for(users)
  .process(async data => {
    // processes 10 items in parallel by default
  })

Bring Your Own Error Handling

The promise pool allows for custom error handling. You can take over the error handling by implementing an error handler using the .handleError(handler).

If you provide an error handler, the promise pool doesn’t collect any errors. You must then collect errors yourself.

Providing a custom error handler allows you to exit the promise pool early by throwing inside the error handler function. Throwing errors is in line with Node.js error handling using async/await.

try {
  const errors = []

  const { results } = await PromisePool
    .for(users)
    .withConcurrency(4)
    .handleError(async (error, user) => {
      if (error instanceof ValidationError) {
        errors.push(error) // you must collect errors yourself
        return
      }

      if (error instanceof ThrottleError) { // Execute error handling on specific errors
        await retryUser(user)
        return
      }

      throw error // Uncaught errors will immediately stop PromisePool
    })
    .process(async data => {
      // the harder you work for something,
      // the greater you’ll feel when you achieve it
    })

  await handleCollected(errors) // this may throw

  return { results }
} catch (error) {
  await handleThrown(error)
}

Contributing

1. Create a fork
2. Create your feature branch: git checkout -b my-feature
3. Commit your changes: git commit -am 'Add some feature'
4. Push to the branch: git push origin my-new-feature
5. Submit a pull request 🚀

License

MIT © Supercharge

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