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https://github.com/hash-bang/async-chainable

An extension to Async adding better handling of mixed Series / Parallel tasks via object chaining
https://github.com/hash-bang/async-chainable

async async-chainable asynchronous callback hooks javascript parallel-tasks

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An extension to Async adding better handling of mixed Series / Parallel tasks via object chaining

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README 

        
async-chainable

===============

Flow control for NodeJS applications.



This builds on the foundations of the [Async](https://www.npmjs.com/package/async) library while adding better handling of mixed Series / Parallel tasks via object chaining.



```javascript

var asyncChainable = require('async-chainable');



asyncChainable() // <- Note '()' as this module is not stateless

	.parallel([fooFunc, barFunc, bazFunc]) // Do these operations in parallel THEN

	.series([fooFunc, barFunc, bazFunc]) // Do these in series (NOTE: these only run when the above has resolved)

	.end(console.log)



asyncChainable()

	.limit(2) // Allow only 2 defer items to run at once from this point on

	.defer('foo', fooFunc) // Run this now and continue on...

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we don't care about 'baz' yet

	.then(function() { console.log(this.foo, this.bar) }) // Output: null, {foo: 'foo value', bar: 'bar value'}

	.await() // Wait for everything else

	.end(function() { console.log(this) }) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}



asyncChainable()

	.parallel('foo', fooFunc)

	.prereq('foo', 'bar', barFunc) // Only let this function run when 'foo' has completed

	.prereq(['foo', 'bar'], 'baz', bazFunc) // Only let this function run when both 'foo' and 'bar' have completed

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}



asyncChainable()

	.forEach([

		'What do we want?',

		'Race conditions!',

		'When do we want them?',

		'Whenever!',

	], function(next, item) {

		// Prints the above array items to the console in parallel (i.e. whichever resolve first - no gurenteed order)

		console.log(item);

		next();

	})

	.end();



// Or use contexts (i.e. `this`) - see Contexts section for more information

asyncChainable()

	.parallel({

		foo: fooFunc,

		bar: barFunc,

		baz: bazFunc

	})

	.then(function(next) {

		console.log(this); // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value', /* META INFO */}

		console.log('Foo =', this.foo); // Output: 'Foo = ', 'foo value'

		next();

	})

	.end();



// Call in stages without chaining

var tasks = asyncChainable();



tasks.defer('foo', fooFunc);



tasks.defer('bar', barFunc);



if (/* some internal logic */) {

	tasks.defer('bar', 'baz', bazFunc); // Only start 'baz' when 'bar' has completed

}



tasks.end(); // Kick everything off



// Specify prerequisites and let async-chainable figure everything out automatically

// This style replaces async.auto() which is a bit ugly



asyncChainable()



	// Task 'foo' relies on 'quz'

	.defer('quz', 'foo', function(next) { next(null, 'fooValue') })



	// Task 'bar' relies on 'baz' and 'foo'

	.defer(['baz', 'foo'], 'bar', function(next) { next(null, 'barValue') })



	// Task 'bar' doesnt need any pre-requisites

	.defer('baz', function(next) { next(null, 'bazValue') })



	// Task 'quz' relies on 'baz'

	.defer('baz', 'quz', function(next) { next(null, 'quzValue') })

	

	// Wait for everything to finish

	.await()

	.end();



// Use async-chainable within ExpressJS

// This example provides an `/order/123` style URL where the order is fetched and returned as a JSON object



app.get('/order/:id', function(req, res) {

	asyncChainable()

		.then(function(next) { // Sanity checks

			if (!req.params.id) return next('No ID specified');

			next();

		})

		.then('order', function(next) { // Fetch order into this.order

			Orders.findOne({_id: req.params.id}, next);

		})

		.then(function(next) {

			// Do something complicated

			setTimeout(next, 1000);

		})

		.end(function(err) {

			if (err) return res.status(400).send(err);

			res.send(this.order);

		});

});

```



Project Goals

=============

This project has the following goals:



* Be semi-compatible with the [Async](https://www.npmjs.com/package/async) library so existing applications are portable over time

* Provide a readable and dependable model for asynchronous tasks

* Have a 'sane' ([YMMV](http://tvtropes.org/pmwiki/pmwiki.php/Main/YMMV)) syntax that will fit most use cases

* Have an extendible plugin system to allow [additional components](#plugins) to be easily brought into the project

* Work with any async paradigm - callbacks, async functions, promises etc.



Plugins

=======

There are a number of async-chainable plugins available which can extend the default functionality of the module:



* [async-chainable-cartesian](https://github.com/hash-bang/async-chainable-cartesian) - Compare large numbers of records against one another

* [async-chainable-compat](https://github.com/hash-bang/async-chainable-compat) - [Async](https://www.npmjs.com/package/async) compatibility layer

* [async-chainable-exec](https://github.com/hash-bang/async-chainable-exec) - External program support

* [async-chainable-flush](https://github.com/hash-bang/async-chainable-flush) - Wait for streams to flush before continuing

* [async-chainable-log](https://github.com/hash-bang/async-chainable-log) - Simple logging extension

* [async-chainable-nightmare](https://github.com/hash-bang/async-chainable-nighmare) - Wrapper around [Nightmare](https://github.com/segmentio/nightmare) to automate a scriptable browser

* [async-chainable-progress](https://github.com/hash-bang/async-chainable-progress) - Adds progress bars, spinners, tick lists and other widgets for long running task chains



FAQ

===

Some frequently asked questions:



* **Why not just use Async?** - Async is an excellent library and suitable for 90% of tasks out there but it quickly becomes unmanageable when dealing with complex nests such as a mix of series and parallel tasks.



* **Why was this developed?** - Some research I was doing involved the nesting of ridiculously complex parallel and series based tasks and Async was becoming more of a hindrance than a helper.



* **What alternatives are there to this library?** - The only ones I've found that come close are [node-seq](https://github.com/substack/node-seq) and [queue-async](https://www.npmjs.com/package/queue-async) but both of them do not provide the functionality listed here



* **Is this the module I should use for Async JavaScript?** - If you're doing simple parallel or series based tasks use [Async](https://www.npmjs.com/package/async), if you're doing complex nested operations you might want to take a look at this one



* **Whats license do you use?** - We use the [MIT license](LICENSE), please credit the original library and authors if you wish to fork or share



* **Who wrote this / who do I blame?** - [Matt Carter](https://github.com/hash-bang) and [David Porter](https://github.com/DesertLynx)



More complex examples

=====================



```javascript

var asyncChainable = require('async-chainable');



// Simple nesting of series and parallel operations

asyncChainable()

	// The following 3 functions execute in series

	.series([

		function(next) { setTimeout(function() { console.log('Series 1'); next(); }, 100); },

		function(next) { setTimeout(function() { console.log('Series 2'); next(); }, 200); },

		function(next) { setTimeout(function() { console.log('Series 3'); next(); }, 300); },

	])



	// ...then we run this...

	.then(function(next) {

		console.log('Finished step 1');

	})



	// ...then the next three run in parallel

	.parallel([

		function(next) { setTimeout(function() { console.log('Parallel 1'); next(); }, 300); },

		function(next) { setTimeout(function() { console.log('Parallel 2'); next(); }, 200); },

		function(next) { setTimeout(function() { console.log('Parallel 3'); next(); }, 100); },

	])

	.end(function(next) {

		console.log('Finished simple example');

	});



// Parameters can be passed by using named functions



asyncChainable()

	.series({ // Since this is node we can KINDA rely on it storing the hash in the right order, don't splice or alter the hash past declaring it though or this functionality will break. Alternatively use the below syntax

		foo: function(next) {

			setTimeout(function() { console.log('Series 2-1'); next(null, 'foo result'); }, 100);

		},

		bar: function(next, results) {

			// We can access results from any function

			setTimeout(function() { console.log('Series 2-2'); next(null, 'bar result'); }, 100);

		},

		baz: function(next) {

			setTimeout(function() { console.log('Series 2-3'); next(null, 'baz result'); }, 100);

		},

	})

	.parallel({ // See above comment about Node storing hashes in the right accessible order

		fooParallel: function(next) {

			setTimeout(function() { console.log('Series 2-1'); next(null, 'foo parallel result'); }, 100);

		},

		barParallel: function(next) {

			setTimeout(function() { console.log('Series 2-2'); next(null, 'bar parallel result'); }, 100);

		},

		bazParallel: function(next) {

			setTimeout(function() { console.log('Series 2-3'); next(null, 'baz parallel result'); }, 100);

		},

	})

	.then(function(next, results) {

		// We also get all the results at the end

		console.log("Results", results); // results = {foo: 'foo result', bar: 'bar result'... 'fooParallel': 'foo parallel result'...}

	})

	.reset() // Or we can clear out the results manually

	.end(function(next, results) {

		console.log('Results should be blank', results);

	};



// In the below examples we assume fooFunc, barFunc, bazFunc and quzFunc functions look something like this:

fooFunc = barFunc = bazFunc = quzFunc = function(next) {

	setTimeout(function() {

		next(null, arguments.callee.toString().substr(0, 3) + ' value'); // Continue on with 'foo value', 'bar value' etc.

	}, Math.random() * 1000); // After a random wait of up to a second

};



// Alternative syntaxes

// All of the below are syntactically the same and will output null, 'foo', 'bar', 'baz (first value is error)

// In each we assume 'series' is the rule but 'parallel' could be substituted if we don't care about sequence

// In each case we have named the functions (e.g. 'foo') but we could just omit this and have a function if we don't care about the result



// Hash style syntax

// NOTE: This relies on the hash not changing order of the keys which is a bit of an issue if you're adding / removing from it out of sequence

asyncChainable()

	.series({foo: fooFunc, bar: barFunc, baz: bazFunc})

	.end(console.log);



// Named function style syntax - series only

asyncChainable()

	.then('foo', fooFunc)

	.then('bar', barFunc)

	.then('baz', bazFunc)

	.end(console.log);



// Named function style syntax - parallel only

asyncChainable()

	.defer('foo', fooFunc) // Start this function immediately and continue on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await() // Resolve all deferred functions before continuing

	.end(console.log);



// Named function style syntax - parallel only

// This works the same as above where if parallel() is NOT passed a hash or array it will act as if called with defer()

asyncChainable()

	.parallel('foo', fooFunc) // Start this function immediately and continue on

	.parallel('bar', barFunc)

	.parallel('baz', bazFunc)

	.await() // Resolve all deferred functions before continuing

	.end(console.log);



asyncChainable()

	.limit(2) // Allow only 2 defer operations to run at once

	.defer('foo', fooFunc)

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we don't care about 'baz' yet

	.then(console.log) // Output: null, {foo: 'foo value', bar: 'bar value'}

	.await() // Wait for everything else

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}



// Classic asyncChainable functionality is still available



asyncChainable()

	.waterfall([

		function(next) { next(null, 'foo') };

		function(next, fooResult) { console.log(fooResult); next(); } // Output = 'foo'

	]);

```



API

===



.await()

--------

Wait for one or more fired defer functions to complete before containing down the asyncChainable chain.



	await() // Wait for all defered functions to finish

	await(string) // Wait for at least the named defer to finish

	await(string,...) // Wait for the specified named defers to finish

	await(array) // Wait for the specified named defers to finish



Some examples:



```javascript

// Wait for everything

asyncChainable()

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await() // Wait for all defers to finish

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}



// Wait for certain defers

asyncChainable()

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we dont care about 'baz' yet

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value'}



// Wait for certain defers - array syntax

asyncChainable()

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await(['foo', 'bar']) // Wait for 'foo' and 'bar' parallel functions to finish but we dont care about 'baz' yet

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value'}

```



.context()

----------

Set the context used by async-chainable during subsequent function calls.

In effect this sets what `this` is for each call.

Omitting an argument or supplying a 'falsy' value will instruct async-chainable to use its own default context object.



```javascript

asyncChainable()

	.then({foo: fooFunc}) // `this` is async-chainables own context object

	.context({hello: 'world'})

	.then({bar: barFunc}) // `this` is now {hello: 'world'}

	.context()

	.then({baz: bazFunc}) // `this` is now async-chainables own context object again

	.end(this) // Output: null, {foo: 'foo value', bar: 'bar value', quz: 'quz value'}

```



Note that even if the context is switched async-chainable still stores any named values in its own context for later retrieval (in the above example this is `barFunc()` returning a value even though the context has been changed to a custom object).



See the [Context Section](#context) for further details on what the async-chainable context object contains.



.defer()

--------

Execute a function and continue down the asyncChainable chain.



	defer(function)

	defer(string, function) // Named function (`this.name` gets set to whatever gets passed to `next()`)

	defer(string, string, function) // Named function (name is second arg) with prereq (first arg)

	defer(array, function) // Run an anonymous function with the specified pre-reqs

	defer(array, string, function) // Named function (name is second arg) with prereq array (first arg)

	defer(string, array, function) // Name function (name is first, prereqs second) this is a varient of the above which matches the `gulp.task(id, prereq)` syntax

	defer(array)

	defer(object) // Named function object (each object key gets assigned to this with the value passed to `next()`)

	defer(collection) // See 'object' definition

	defer(null) // Gets skipped automatically



Use `await()` to gather the parallel functions.

This can be considered the parallel process twin to `series()` / `then()`.



```javascript

asyncChainable()

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we dont care about 'baz' yet

	.then(console.log) // Output: null, {foo: 'foo value', bar: 'bar value'}

	.await() // Wait for everything else

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}

```



**NOTE**: All defers take their 'next' handler as the first argument. All subsequent arguments are the resolved value of the prerequisites. In the above example `barFunc` would be called as `barFunc(next, resultOfFoo)` and `bazFunc` would be called as `bazFunc(next, resultOfBaz)`.



.end()

------

The final stage in the chain, `.end()` must be called to execute the queue of actions.



	end() // Run the chain but don't do anything when completed

	end(function) // Final function to execute as `function(err)`

	end(string, function) // Extract the context value specified by string and provide it to the callback 



NOTE: The form `end(string, function)` is used  is the internal equivalent to `end(err => callback(err, this[string]))` - i.e. the context value is extracted for you.



While similar to `series()` / `then()` this function will always be executed *last* and be given the error if any occurred in the form `function(err)`.



```javascript

asyncChainable()

	.then('foo', fooFunc) // Execute and wait for fooFunc() to complete

	.then('bar', barFunc) // Likewise barFunc()

	.then('baz', bazFunc) // Likewise bazFunc()

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}

```



In the above if fooFunc, barFunc or bazFunc call next with a first parameter that is true execution will stop and continue on passing the error to `end()`:



```javascript

asyncChainable()

	.then('foo', fooFunc) // Assuming fooFunc calls next('This is an error')

	.then('bar', barFunc) // Gets skipped as we have an error

	.then('baz', bazFunc) // Gets skipped as we have an error

	.end(console.log) // Output: 'This is an error'

```



If an error is caused in the middle of execution the result object is still available:



```javascript

asyncChainable()

	.then('foo', fooFunc) // Assuming this calls `next()` with next(null, 'foo value')

	.then('bar', barFunc) // Assuming this calls next('Error in bar')

	.then('baz', bazFunc) // Gets skipped as we have an error

	.end(console.log) // Output: 'Error in bar', {foo: 'foo value'}

```



.fire()

-------

Trigger a hook. This function will run a callback on completion whether or not any hooks executed.



	fire(string, function) // Fire a hook and run the callback on completion

	this.fire(...) // Same as above invocations but accessible within a chain



```javascript

asyncChainable()

	.forEach(['foo', 'bar', 'baz'], function(next, item, key) { console.log(item) }) // Output: foo, bar and baz in whichever they evaluate

	.hook('hello', function(next) { console.log('Hello world!'); next() })

	.then(function(next) {

		// Trigger a hook then continue on

		this.fire('hello, next);

	})

	.end();

```



.forEach()

----------

The `forEach()` function is a slight variation on the `parallel()` function but with some additional behaviour.



	forEach(fromNumber, toNumber, function) // Call function toNumber-fromNumber times

	forEach(toNumber, function) // Call function toNumber times (same as `forEach(1, NUMBER, function)`)

	forEach(array, function) // Run each item in the array though `function(next, value)`

	forEach(object, function) // Run each item in the object though `function(next, value, key)`

	forEach(collection,function) // see 'array, function' definition (collections are just treated like an array of objects with 'forEach')

	forEach(string, function) // Lookup `this[string]` then process according to its type (see above type styles) - This is used for late binding

	forEach(string, array, function) // Perform a map operation on the array setting the `this[string]` to the ordered result return

	forEach(string, object, function) // Perform a map operation on an object array setting the `this[string]` to the result return

	forEach(string, string, function) // Lookup the first string and process it as a map operation according to its type (see above 2 examples) - This is used for late binding

	forEach(null) // Gets skipped automatically (also empty arrays, objects)



It can be given an array, object or collection as the first argument and a function as the second. All items in the array will be iterated over *in parallel* and passed to the function which is expected to execute a next condition returning an error if the forEach iteration should stop.



```javascript

asyncChainable()

	.forEach(['foo', 'bar', 'baz'], function(next, item, key) { console.log(item) }) // Output: foo, bar and baz in whichever they evaluate

	.end();

```



In the above example the simple array is passed to the function with each payload item as a parameter and the iteration key (an offset if its an array or collection, a key if its an object).



`forEach()` has one additional piece of behaviour where if the first argument is a string the context will be examined for a value to iterate over. The string can be a simple key to use within the passed object or a deeply nested path using dotted notation (e.g. `key1.key2.key3`).



```javascript

asyncChainable()

	.set({

		items: ['foo', 'bar', 'baz'],

	})

	.forEach('items', function(next, item, key) { console.log(item); next() }) // Output: foo, bar and baz in whichever order they evaluate

	.end();

```



This allows *late binding* of variables who's content will only be examined when the chain item is executed.



.getPath()

----------

GetPath is the utility function used by `forEach()` to lookup deeply nested objects or arrays to iterate over.

It is functionally similar to the Lodash `get()` function.



.hook()

-------

Attach a callback hook to a named trigger. These callbacks can all fire errors themselves and can fire out of sequence, unlike normal chains.

Hooks can be defined multiple times - if multiple callbacks are registered they are fired in allocation order in *series*. If any hook raises an error the chain is terminated as though a callback raised an error.

Defined hooks can be `start`, `end`, `timeout` as well as any user-defined hooks.

Hooks can also be registered within a callback via `this.hook(hook, callback)` unless context is reset.

Hooks can also have an optional id and an array of prerequisites



	hook(string, function) // Register a callback against a hook

	hook(array, function) // Register a callback against a number of hooks, if any fire the callback is called

	hook(string, string, function) // Register a named hook

	hook(string, array, function) // Register a hook with prerequisites

	hook(string, string, array, function) // Register a named hook with an array of prerequisite hooks

	this.hook(...) // Same as above invocations but accessible within a chain



```javascript

asyncChainable()

	.forEach(['foo', 'bar', 'baz'], function(next, item, key) { console.log(item) }) // Output: foo, bar and baz in whichever they evaluate

	.hook('start', function(next) { console.log('Start!'); next()  })

	.hook('end', function(next) { console.log('End!'); next()  })

	.hook(['start', 'end'], function(next) { console.log('Start OR End!'); next()  })

	.end();

```



.limit()

--------

Restrict the number of defer operations that can run at any one time.



	limit() // Allow unlimited parallel / defer functions to execute at once after this chain item

	limit(Number) // Restrict the number of parallel / defer functions after this chain item



This function can be used in the pipeline as many times as needed to change the limit as we work down the execution chain.



```javascript

asyncChainable()

	.limit(2) // Allow only 2 defer operations to run at once from this point onward

	.defer(fooFunc)

	.defer(barFunc)

	.defer(bazFunc)

	.defer(quzFunc)

	.await()

	.limit(3) // Allow 3 defer operations to run at once from this point onward

	.defer(fooFunc)

	.defer(barFunc)

	.defer(bazFunc)

	.defer(quzFunc)

	.await()

	.limit() // Allow unlimited operations to run at once from this point onward (0 / false / null is also permissable as 'unlimited')

	.defer(fooFunc)

	.defer(barFunc)

	.defer(bazFunc)

	.defer(quzFunc)

	.await()

	.end(console.log)

```



.map()

------

The `map()` function is really just an alias for `forEach()` aimed specifically at the following functions:



	map(string, array, function) // Perform a map operation on the array setting the `this[string]` to the ordered result return

	map(string, object, function) // Perform a map operation on an object array setting the `this[string]` to the result return

	map(string, string, function) // Lookup the first string and process it as a map operation according to its type (see above 2 examples) - This is used for late binding



**NOTES:**



* Each function is expected to return a result which is used to compose the new object / array.

* The object return type can also specify an alternate key as the third parameter to the callback (i.e. `callback(error, valueReturn, keyReturn)`). If unspecified the original key is used, if specified it is used instead of the original.

* Late binding maps can accept the same input and output key name in order to overwrite the original.



See the [test files](./test/map.js) for more examples.



.promise()

----------

Alternative to `end()` which returns a JS standard promise instead of using the `.end(callback)` system.



	promise() // Return a promise which will resolve with no value

	promise(string) // Return a promise which will return with the extracted context value

	promise(function) // Return a promise but also run a callback

	promise(string, function) // Extract the context value specified by string and provide it to the callback 



```javascript

asyncChainable()

	.then(doSomethingOne)

	.then(doSomethingTwo)

	.then(doSomethingThree)

	.promise()

	.then(function() { // Everything went well })

	.catch(function(err) { // Something went wrong })

```



.race()

-------

Run multiple functions setting the named key to the first function to return with a non-null, non-undefined value.

If an error is thrown *before or after* the result is achived it will be returned instead.



```javascript

asyncChainable()

	.race('myKey', [

		fooFunc,

		barFunc,

		bazFunc,

	])

	.end(function(err) {

		console.log('myKey =', this.myKey);

	});

```



.reset()

---------

Clear the result buffer, releasing all results held in memory.



```javascript

asyncChainable()

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we dont care about 'baz' yet

	.then(console.log) // Output: null, {foo: 'foo value', bar: 'bar value'}

	.reset()

	.defer('quz', quzFunc)

	.end(console.log) // Output: null, {quz: 'quz value'}

```



.run()

------

Internal function to resolve a function, async function, promise etc. etc. and then run a callback.



	run([context], fn, cb, [args])



.runArray()

------

Internal callback resolver. Run is used to execute an array of callbacks then run a final callback. This function is NOT chainable, will execute immediately and is documented here as it is useful when writing plugins.



	runArray(array, limit, callback)



.runWhile()

------

Internal callback resolver until a function returns falsy. This function is NOT chainable, will execute immediately and is documented here as it is useful when writing plugins.

Unlike `runArray()` this function does not require a precomputed array of items to iterate over which makes it a kind of generator function useful for potencially large data set iterations.



	runWhile(function(next, index) {}, limit, callback)



.series() / .parallel()

-----------------------

Execute an array or object of functions either in series or parallel.



	series(function)

	series(string, function) // Named function (`this.name` gets set to whatever gets passed to `next()`)

	series(array)

	series(object) // Named function object (each object key gets assigned to this with the value passed to `next()`)

	series(collection) // See 'object' definition

	series(array, function) // Backwards compatibility with `async.series`

	series(object, function) // Backwards compatibility with `async.series`



	parallel(function)

	parallel(string, function) // Named function (`this.name` gets set to whatever gets passed to `next()`)

	parallel(array)

	parallel(object) // Named function object (each object key gets assigned to this with the value passed to `next()`)

	parallel(collection) // See 'object' definition

	parallel(array, function) // Backwards compatibility with `parallel.series`

	parallel(object, function) // Backwards compatibility with `parallel.series`



Some examples:



```javascript

asyncChainable()

	.parallel(Array) // Execute all items in the array in parallel

	.parallel(Object) // Execute all items in the object in parallel storing any return against the object key

	.parallel(Collection) // i.e. an array of objects - this is to work around JS not maintaining hash key orders

	.parallel(String, function) // Execute function now and await output, then store in object against key specified by String

	.parallel(function) // Exactly the same functionality as `defer()`

	.end()



asyncChainable()

	.series(Array) // Execute all items in the array in parallel

	.series(Object) // Execute all items in the object in series storing any return against the object key

	.series(Collection) // i.e. an array of objects - this is to work around JS not maintaining hash key orders

	.series(String, function) // Execute function now and await output, then store in object against key specified by String

	.series(function) // Exactly the same functionality as `then()`

	.end()

```



.set()

------

Set is a helper function to quickly allocate the value of a context item as we move down the chain.



	set(string, mixed) // Set the single item in `this` specified the first string to the value of the second arg

	set(object) // Merge the object into `this` to quickly set a number of values

	set(function) // Alias for `series(function)`

	set(string, function) // Alias for `series(string, function)`



It can be used as a named single item key/value or as a setter object.



```javascript

asyncChainable()

	.set('foo', 'foo value')

	.then(function(next) { console.log(this.foo); next() }) // this.foo is now 'foo value'

	.set({bar: 'bar value'}) 

	.then(function(next) { console.log(this.foo); next() }) // this.bar is now 'bar value' (as well as .foo being also set)

	.set(baz, function(next) { next(null, 'baz value') }) // this.baz is now 'baz value' (this is actually just an alias for .series())

	.then(function(next) { console.log(this.foo); next() }) // this.baz is now 'baz value' (as well as .foo, .bar being also set)

	.end()

```



.timeout()

----------

Set a delay and/or a callback to run if the Async chain goes over a specified timeout.



	timeout(number) // Set the timeout delay

	timeout(number, function) // Set the timeout delay + a callback

	timeout(function) // Set the timeout callback

	timeout(false) // Disable timeouts



```javascript

asyncChainable()

	.timeout(100, function() {

		console.log('Timer went over 100ms!');

	})

	.then(function(next) {

		setTimeout(next, 2000); // Take 2 seconds

	})

	.end()

```



NOTE: Timeouts will also fire the `timeout` hook if the timeout function is the default (i.e. the user hasn't changed the function to their own).



.then()

-------

Execute a function, wait for it to complete and continue down the asyncChainable chain.



This function is an alias for `series()`.



This can be considered the series process twin to `then()`.



```javascript

asyncChainable()

	.then('foo', fooFunc) // Execute and wait for fooFunc() to complete

	.then('bar', barFunc) // Likewise barFunc()

	.then('baz', bazFunc) // Likewise bazFunc()

	.end(console.log) // Output: null, {foo: 'foo value', bar: 'bar value', baz: 'baz value'}

```



Context

=======

Unless overridden by a call to `.context()`, async-chainable will use its own context object which can be accessed via `this` inside any callback function.

The context contains the results of any *named* functions as well as some meta data.



```javascript

asyncChainable()

	.series('foo', fooFunc)

	.defer('foo', fooFunc) // Execute fooFunc() and immediately move on

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await('foo', 'bar') // Wait for 'foo' and 'bar' parallel functions to finish but we dont care about 'baz' yet

	.then(function(next) {

		console.log('Context is', this); // Output 'Context is', {foo: 'foo value', bar: 'bar value', /* META FIELDS */}

		next();

	})

	.await('baz')

	.end(function(next) {

		console.log('Context is', this); // Output 'Context is', {foo: 'foo value', bar: 'bar value', baz: 'baz value', /* META FIELDS */}

		next();

	});

```



In addition to storing all named values the context object also provides the following meta object values.



| Key                                  | Type           |  Description                                                             |

|--------------------------------------|----------------|--------------------------------------------------------------------------|

| `this._struct`                       | Collection     | The structure of the async chain constructed by the developer            |

| `this._structPointer`                | Int            | Offset in the `this._struct` collection as to the current executing function. Change this if you wish to move up and down |

| `this._options`                      | Object         | Various options used by async-chainable including things like the defer limit |

| `this._deferredRunning`              | Int            | The number of running deferred tasks (limit this using .limit())         |

| `this._item`                         | Mixed          | During a forEach loop `_item` gets set to the currently iterating item value |

| `this._key`                          | Mixed          | During a forEach loop `_key` gets set to the currently iterating array offset or object key |

| `this._id`                           | Mixed          | During a defer call `_id` gets set to the currently defered task id      |

| `this.fire`                          | Function       | Utility function used to manually fire hooks                             |

| `this.hook`                          | Function       | Utility function used to manually register a hook                        |



Each item in the `this._struct` object is composed of the following keys:



| Key                                  | Type           |  Description                                                             |

|--------------------------------------|----------------|--------------------------------------------------------------------------|

| `completed`                          | Boolean        | An indicator as to whether this item has been executed yet               |

| `payload`                            | Mixed          | The options for the item, in parallel or series modes this is an array or object of the tasks to execute |

| `type`                               | String         | A supported internal execution type                                      |

| `waitingOn`                          | Int            | When the type is a defer operation this integer tracks the number of defers that have yet to resolve |



Gotchas

=======

A list of some common errors when using async-chainable.



Forgetting a final `await()` when using `end()`

-----------------------------------------------



By default async-chainable will not *imply* an `.await()` call before each `.end()` call. For example:



```javascript

asyncChainable()

	.defer('foo', fooFunc)

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.end(console.log);

```



In the above no `.await()` call is made before `.end()` so this chain will *immediately* complete - async-chainable will **not** wait for the deferred tasks to complete.



```javascript

asyncChainable()

	.defer('foo', fooFunc)

	.defer('bar', barFunc)

	.defer('baz', bazFunc)

	.await()

	.end(console.log);

```



In the above async-chainable will wait for the deferred tasks to complete before firing the end condition.



Forgetting the `()` when initializing

-------------------------------------

Async-chainable needs to store state as it processes the task stack, to do this it instantiates itself as an object. This means you must declare it with an additional `()` after the `require()` statement if you wish to use it straight away. For example:



```javascript

var asyncChainable = require('async-chainable')(); // NOTE '()'



asyncChainable()

	.parallel([fooFunc, barFunc, bazFunc])

	.series([fooFunc, barFunc, bazFunc])

	.end(console.log)

```



If you want to use multiple instances you can use either:



```javascript

var asyncChainable = require('async-chainable'); // NOTE: this returns the libray not the instance



asyncChainable()

	.parallel([fooFunc, barFunc, bazFunc])

	.series([fooFunc, barFunc, bazFunc])

	.end(console.log)



asyncChainable()

	.parallel([fooFunc, barFunc, bazFunc])

	.series([fooFunc, barFunc, bazFunc])



	.end(console.log)

```



Its annoying we have to do this but without hacking around how Nodes module system works its not possible to return a singleton object like the async library does *and also* work with nested instances (i.e. having one .js file require() another that uses async-chainable and the whole thing not end up in a messy stack trace as the second instance inherits the firsts return state).



Useful techniques

=================



Debugging

---------

If you find that async-chainable is hanging try setting a `.timeout()` on the object to be notified when something is taking a while.



For one off operations async-chainable will also respond to the `DEBUG=async-chainable` environment variable. For example running your script as:



	DEBUG=async-chainable node myscript.js



... will automatically set a `.timeout(5000)` call on **all** async-chainable objects with the default timeout handler (which should give some useful information on anything that is hanging).



Make a variable number of tasks then execute them

-------------------------------------------------

Since JavaScript passes everything via pointers you can pass in an array or object to a .parallel() or .series() call which will get evaluated only when that chain item gets executed. This means that preceding items can rewrite the actual tasks conducted during that call.



For example in the below `otherTasks` is an array which is passed into the .parallel() call (the second chain item). However the initial .then() callback actually writes the items that that parallel call should make.



```javascript

var otherTasks = [];



asyncChainable()

	.then(function(next) {

		for (var i = 0; i < 20; i++) {

			(function(i) { // Make a closure so 'i' doesnt end up being 20 all the time (since its passed by reference)

				otherTasks.push(function(next) {

					console.log('Hello World', i);

					next();

				});

			})(i);

		}

		next();

	})

	.parallel(otherTasks)

	.end();

```



Compose an array of items then run each though a handler function

-----------------------------------------------------------------

Like the above example async-chainable can be used to prepare items for execution then thread them into a subsequent chain for processing.

This is a neater version of the above that uses a fixed processing function to process an array of data.



```javascript

var asyncChainable = require('./index');



var items = [];



asyncChainable()

	.then(function(next) {

		for (var i = 0; i < 20; i++) {

			items.push({text: 'Hello World ' + i});

		}

		next();

	})

	.forEach(items, function(next, item) {

		console.log(item);

		next();

	})

	.end();

```