CHANGELOG.md

v2.0.0

Lots of changes here! The biggest feature is modularization. You can now require("async/series") to only require the series function. Every Async library function is available this way. You still can require("async") to require the entire library, like you could do before.

We also provide Async as a collection of ES2015 modules. You can now import {each} from 'async-es' or import waterfall from 'async-es/waterfall'. If you are using only a few Async functions, and are using a ES bundler such as Rollup, this can significantly lower your build size.

Major thanks to @Kikobeats, @aearly and @megawac for doing the majority of the modularization work, as well as @jdalton and @Rich-Harris for advisory work on the general modularization strategy.

Another one of the general themes of the 2.0 release is standardization of what an "async" function is. We are now more strictly following the node-style continuation passing style. That is, an async function is a function that:

1. Takes a variable number of arguments
2. The last argument is always a callback
3. The callback can accept any number of arguments
4. The first argument passed to the callback will be treated as an error result, if the argument is truthy
5. Any number of result arguments can be passed after the "error" argument
6. The callback is called once and exactly once, either on the same tick or later tick of the JavaScript event loop.

There were several cases where Async accepted some functions that did not strictly have these properties, most notably auto, every, some, and filter.

Another theme is performance. We have eliminated internal deferrals in all cases where they make sense. For example, in waterfall and auto, there was a setImmediate between each task -- these deferrals have been removed. A setImmediate call can add up to 1ms of delay. This might not seem like a lot, but it can add up if you are using many Async functions in the course of processing a HTTP request, for example. Nearly all asynchronous functions that do I/O already have some sort of deferral built in, so the extra deferral is unnecessary. The trade-off of this change is removing our built-in stack-overflow defense. Many synchronous callback calls in series can quickly overflow the JS call stack. If you do have a function that is sometimes synchronous (calling its callback on the same tick), and are running into stack overflows, wrap it with async.ensureAsync().

New Features

• Async is now modularized. Individual functions can be require()d from the main package. (require('async/auto')) (#984, #996)
• Async is also available as a collection of ES2015 modules in the new async-es package. (import {forEachSeries} from 'async-es') (#984, #996)
• Added race, analogous to Promise.race(). It will run an array of async tasks in parallel and will call its callback with the result of the first task to respond. (#568, #1038)
• Added timeout, a wrapper for an async function that will make the task time-out after the specified time. (#1007, #1027)
• constant supports dynamic arguments -- it will now always use its last argument as the callback. (#1016, #1052)
• setImmediate and nextTick now support arguments to partially apply to the deferred function, like the node-native versions do. (#940, #1053)
• Added autoInject, a relative of auto that automatically spreads a task's dependencies as arguments to the task function. (#608, #1055)
• You can now limit the concurrency of auto tasks. (#635, #637)
• Added retryable, a relative of retry that wraps an async function, making it retry when called.
• Added q.unsaturated -- callback called when a queue's number of running workers falls below a threshold. (#868, #1030, #1033, #1034)

Breaking changes

• Calling a callback more than once is considered an error, and an error will be thrown. This had an explicit breaking change in waterfall. If you were relying on this behavior, you should more accurately represent your control flow as an event emitter or stream. (#814, #815, #1048, #1050)
• auto task functions now always take the callback as the last argument. If a task has dependencies, the results object will be passed as the first argument. To migrate old task functions, wrap them with _.flip (#1036, #1042)
• Internal setImmediate calls have been refactored away. This may make existing flows vulnerable to stack overflows if you use many synchronous functions in series. Use ensureAsync to work around this. (#696, #704, #1049, #1050)
• filter, reject, some, every, and related functions now expect an error as the first callback argument, rather than just a simple boolean. Pass null as the first argument, or use fs.access instead of fs.exists. (#118, #774, #1028, #1041)
• {METHOD} and {METHOD}Series are now implemented in terms of {METHOD}Limit. This is a major internal simplification, and is not expected to cause many problems, but it does subtly affect how functions execute internally. (#778, #847)
• retry's callback is now optional. Previously, omitting the callback would partially apply the function, meaning it could be passed directly as a task to series or auto. The partially applied "control-flow" behavior has been separated out into retryable.

Other

• Added someSeries and everySeries for symmetry, as well as a complete set of any/anyLimit/anySeries and all//allLmit/allSeries aliases.
• Added find as an alias for detect (as well as findLimit and findSeries).
• Various doc fixes (#1005, #1008, #1010, #1015, #1021, #1037)

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v1.5.2

• Allow using "constructor" as an argument in memoize (#998)
• Give a better error messsage when auto dependency checking fails (#994)
• Various doc updates (#936, #956, #979, #1002)

v1.5.1

• Fix issue with pause in queue with concurrency enabled (#946)
• while and until now pass the final result to callback (#963)
• auto will properly handle concurrency when there is no callback (#966)
• auto will now properly stop execution when an error occurs (#988, #993)
• Various doc fixes (#971, #980)

v1.5.0

• Added transform, analogous to _.transform (#892)
• map now returns an object when an object is passed in, rather than array with non-numeric keys. map will begin always returning an array with numeric indexes in the next major release. (#873)
• auto now accepts an optional concurrency argument to limit the number of running tasks (#637)
• Added queue#workersList(), to retrieve the list of currently running tasks. (#891)
• Various code simplifications (#896, #904)
• Various doc fixes 📜 (#890, #894, #903, #905, #912)

v1.4.2

• Ensure coverage files don't get published on npm (#879)

v1.4.1

• Add in overlooked detectLimit method (#866)
• Removed unnecessary files from npm releases (#861)
• Removed usage of a reserved word to prevent 💥 in older environments (#870)

v1.4.0

• asyncify now supports promises (#840)
• Added Limit versions of filter and reject (#836)
• Add Limit versions of detect, some and every (#828, #829)
• some, every and detect now short circuit early (#828, #829)
• Improve detection of the global object (#804), enabling use in WebWorkers
• whilst now called with arguments from iterator (#823)
• during now gets called with arguments from iterator (#824)
• Code simplifications and optimizations aplenty (diff)

v1.3.0

New Features:

• Added constant
• Added asyncify/wrapSync for making sync functions work with callbacks. (#671, #806)
• Added during and doDuring, which are like whilst with an async truth test. (#800)
• retry now accepts an interval parameter to specify a delay between retries. (#793)
• async should work better in Web Workers due to better root detection (#804)
• Callbacks are now optional in whilst, doWhilst, until, and doUntil (#642)
• Various internal updates (#786, #801, #802, #803)
• Various doc fixes (#790, #794)

Bug Fixes:

• cargo now exposes the payload size, and cargo.payload can be changed on the fly after the cargo is created. (#740, #744, #783)

v1.2.1

Bug Fix:

• Small regression with synchronous iterator behavior in eachSeries with a 1-element array. Before 1.1.0, eachSeries's callback was called on the same tick, which this patch restores. In 2.0.0, it will be called on the next tick. (#782)

v1.2.0

New Features:

• Added timesLimit (#743)
• concurrency can be changed after initialization in queue by setting q.concurrency. The new concurrency will be reflected the next time a task is processed. (#747, #772)

Bug Fixes:

• Fixed a regression in each and family with empty arrays that have additional properties. (#775, #777)

v1.1.1

Bug Fix:

• Small regression with synchronous iterator behavior in eachSeries with a 1-element array. Before 1.1.0, eachSeries's callback was called on the same tick, which this patch restores. In 2.0.0, it will be called on the next tick. (#782)

v1.1.0

New Features:

• cargo now supports all of the same methods and event callbacks as queue.
• Added ensureAsync - A wrapper that ensures an async function calls its callback on a later tick. (#769)
• Optimized map, eachOf, and waterfall families of functions
• Passing a null or undefined array to map, each, parallel and families will be treated as an empty array (#667).
• The callback is now optional for the composed results of compose and seq. (#618)
• Reduced file size by 4kb, (minified version by 1kb)
• Added code coverage through nyc and coveralls (#768)

Bug Fixes:

• forever will no longer stack overflow with a synchronous iterator (#622)
• eachLimit and other limit functions will stop iterating once an error occurs (#754)
• Always pass null in callbacks when there is no error (#439)
• Ensure proper conditions when calling drain() after pushing an empty data set to a queue (#668)
• each and family will properly handle an empty array (#578)
• eachSeries and family will finish if the underlying array is modified during execution (#557)
• queue will throw if a non-function is passed to q.push() (#593)
• Doc fixes (#629, #766)

v1.0.0

No known breaking changes, we are simply complying with semver from here on out.

Changes:

• Start using a changelog!
• Add forEachOf for iterating over Objects (or to iterate Arrays with indexes available) (#168 #704 #321)
• Detect deadlocks in auto (#663)
• Better support for require.js (#527)
• Throw if queue created with concurrency 0 (#714)
• Fix unneeded iteration in queue.resume() (#758)
• Guard against timer mocking overriding setImmediate (#609 #611)
• Miscellaneous doc fixes (#542 #596 #615 #628 #631 #690 #729)
• Use single noop function internally (#546)
• Optimize internal _each, _map and _keys functions.