pasync

Version of async that uses promises instead of callbacks. Also includes other asynchronous promise utilities.

var pasync = require('pasync');

function getUserById(id) {
	return new Promise(...);
}

var userIds = [1, 2, 3, 4, 5, 6];

pasync.mapLimit(userIds, 2, getUserById).then(function(users) {
	// ...
});

You can also return values instead of promises from the iterator functions, and these will be converted into resolved promises. Exceptions thrown from iterator functions will be converted into rejected promises.

Additionally, this implements error handling for async functions that don't natively have error handling, such as async.filter .

Implemented Functions

• each
• eachSeries
• eachLimit
• map
• mapSeries
• mapLimit
• mapValues
• mapValuesSeries
• mapValuesLimit
• filter
• select
• filterSeries
• selectSeries
• reject
• rejectSeries
• reduce
• reduceRight
• detect
• detectSeries
• sortBy
• some
• every
• concat
• concatSeries
• series
• parallel
• parallelLimit
• whilst
• doWhilst
• until
• doUntil
• forever
• waterfall
• queue
• compose
• applyEach
• applyEachSeries
• retry
• apply
• nextTick
• times
• timesSeries
• asyncify
• wrapSync
• during
• doDuring

Other Utilities

all([promises])

Note

async.all is an alias for async.every. pasync.all is the function described here, not an alias for every.

This is similar to ES6's Promise.all(), but with the following differences and enhancements:

• The returned promise has a push(promise) method which allows you to add additional promises to the pool after instantiation. The returned promise only resolves once all promises added to it have resolved. It is an error to try to push a new promise after the returned promise has already resolved.
• Promises may be pushed after the returned promises has rejected. In this case, newly pushed promises are silently ignored.
• The order of the result array is guaranteed to be the order that promises were added.
• The [promise1, promise2, ...] parameter is optional. If not passed (or is an empty array), the returned promise will not resolve immediately; instead it will wait for at least one promise to be pushed.

Use it like this:

var p = pasync.all([ promise1, promise2 ]);
p.then(/* handlers */);
// later ...
p.push(promise3);
p.push(promise4);

setTimeout(ms)

Just a promisified javascript setTimeout.

pasync.setTimeout(100).then(function() {
	console.log('Waited 100 milliseconds.');
});

setImmediate()

Same as above, but for setImmediate.

pasync.setImmediate().then(function() {
	console.log('Waited until after I/O event callbacks.');
});

abort(err)

This is intended to be used as a last-ditch error handler for promises. Using promises, if the last rejection handler in a promise throws an exception, it is silently ignored. Calling abort(err) will throw err as an exception in the global scope, calling the process's uncaughtException listeners or exiting with the exception by default. Use it like this:

getUser(nonexistent_id).then(function(user) {
	// do something with user
}).catch(function(err) {
	// Note the (obvious) errors in the rejection handlers; by default, this will be silently ignored
	cunsil.lug(err);
}).catch(pasync.abort);	// This will catch the undefined variable error and throw it globally

waiter()

This returns an object that encapsulates a promise and can be resolved from different contexts. The behavior is as follows:

• promise is the ensapsulated promise, and resolves or rejects when resolve/reject are called.
• resolve(res) resolves the promise. If the encapsulated promise has already resolved or rejected, a new promise is created.
• reject(err) rejects the promise. If the encapsulated promise has already rejected, a new promise is created.
• reset() creates a new unresolved promise if the promise has already been resolved or rejected.

This acts like a deferred, but one where the promise can be re-resolved or re-rejected. If resolve() or reject() are called and the promise has already been resolved/rejected, a new promise is constructed.

var waiter = pasync.waiter();

waiter.promise.then(function(db) {
  db.get(...)
});

waiter.promise.then(function(db) {
  db.get(...)
});

connectToDatabase.then(function(db) {
  waiter.resolve(db);
})

Contributors

• crispy1989
• crowelch