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async-chainable

Flow control functions for NodeJS

async-chainable

Flow control for NodeJS applications.

This builds on the foundations of the Async library while adding better handling of mixed Series / Parallel tasks via object chaining.

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(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'} 
 
 
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 library so existing applications are portable over time
  • Provide a readable and dependable model for asynchronous tasks
  • Have a 'sane' (YMMV) syntax that will fit most use cases
  • Have an extendible plugin system to allow additional components to be easily brought into the project

Plugins

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

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 and 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, 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, please credit the original library and authors if you wish to fork or share

  • Who wrote this / who do I blame? - Matt Carter and David Porter

More complex examples

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

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:

// 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'} 

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.

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 for further details on what the async-chainable context object contains.

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().

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).

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

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

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).

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():

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:

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'} 

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
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();

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
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(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.

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).

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

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

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.

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.

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

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.

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)

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

asyncChainable()
    .then(doSomethingOne)
    .then(doSomethingTwo)
    .then(doSomethingThree)
    .promise()
    .then(function() { // Everything went well }) 
    .catch(function(err) { // Something went wrong }) 

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.

asyncChainable()
    .race('myKey', [
        fooFunc,
        barFunc,
        bazFunc,
    ])
    .end(function(err) {
        console.log('myKey =', this.myKey);
    });

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

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'} 

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.

run(array, limit, callback)

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 run() 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)

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:

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 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.

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()

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
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).

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().

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.

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.

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

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.

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.

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:

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:

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

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).

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.

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();

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.

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();