async v3.0.0 Release Notes

Release Date: 2019-05-20 // about 3 years ago
  • ๐Ÿš€ The async/await release!

    There are a lot of new features and subtle breaking changes in this major version, but the biggest feature is that most Async methods return a Promise if you omit the callback, meaning you can await them from within an async function.

    const results = await async.mapLimit(urls, 5, async url => {
        const resp = await fetch(url)
        return resp.body

    ๐Ÿ’ฅ Breaking Changes

    • Most Async methods return a Promise when the final callback is omitted, making them await-able! (#1572)
    • ๐Ÿ’ป We are now making heavy use of ES2015 features, this means we have dropped out-of-the-box support for Node 4 and earlier, and many old versions of browsers. (#1541, #1553)
    • ๐Ÿ’… In queue, priorityQueue, cargo and cargoQueue, the "event"-style methods, like q.drain and q.saturated are now methods that register a callback, rather than properties you assign a callback to. They are now of the form q.drain(callback). If you do not pass a callback a Promise will be returned for the next occurrence of the event, making them await-able, e.g. await q.drain(). (#1586, #1641)
    • Calling callback(false) will cancel an async method, preventing further iteration and callback calls. This is useful for preventing memory leaks when you break out of an async flow by calling an outer callback. (#1064, #1542)
    • ๐Ÿšš during and doDuring have been removed, and instead whilst, doWhilst, until and doUntil now have asynchronous test functions. (#850, #1557)
    • limits of less than 1 now cause an error to be thrown in queues and collection methods. (#1249, #1552)
    • memoize no longer memoizes errors (#1465, #1466)
    • applyEach/applyEachSeries have a simpler interface, to make them more easily type-able. It always returns a function that takes in a single callback argument. If that callback is omitted, a promise is returned, making it awaitable. (#1228, #1640)

    ๐Ÿ†• New Features

    • ๐Ÿ‘ Async generators are now supported in all the Collection methods. (#1560)
    • โž• Added cargoQueue, a queue with both concurrency and payload size parameters. (#1567)
    • Queue objects returned from queue now have a Symbol.iterator method, meaning they can be iterated over to inspect the current list of items in the queue. (#1459, #1556)
    • ๐Ÿ“ฆ A ESM-flavored async.mjs is included in the async package. This is described in the package.json "module" field, meaning it should be automatically used by Webpack and other compatible bundlers.

    ๐Ÿ› Bug fixes

    • ๐Ÿ‘ Better handle arbitrary error objects in asyncify (#1568, #1569)


    • โœ‚ Removed Lodash as a dependency (#1283, #1528)
    • ๐Ÿ›  Miscellaneous docs fixes (#1393, #1501, #1540, #1543, #1558, #1563, #1564, #1579, #1581)
    • โœ… Miscellaneous test fixes (#1538)