async


https://github.com/caolan/async

Amith Nambiar



async library can be divided into :

  • Collections
  • Control Flow
  • Utility functions

Why async?

  •   async can help  avoid this deep nesting of function calls.
  •   It has many utility functions which work on collections.

Deep nesting of functions within callbacks.







async is a utility module which provides 
straight-forward, powerful functions for working with asynchronous JavaScript.





All these functions assume you follow the node.js convention of providing a single callback as the last argument of your async function.


 function downloadFile(url, callback) {    // download file    callback(err, filedata);  }

                    


                  
                  Around 20 functions that include the usual 
            'functional' suspects (map, reduce,filter) 
                      as well as some common patterns for 
                              asynchronous control flow

"callback hell" example



nonasyncexample.js

See the library in action with the rest of the slides @ https://github.com/amithn/async-examples


async.each(array, iterator, callback)


  • Applies an iterator function to each item in an array, in parallel.  Iterators might not complete in order.

  • The iterator is called with an item from the list and a callback for when it has finished. 

  • If the iterator passes an error to this callback, the main callback  is immediately called with the error.

async.eachSeries(array, iterator, callback)



  • Same as async.each() except for Iterators will complete in order.

async.map(array, iterator, callback)


  • Produces a new array of values by mapping each value in the given array through the iterator function. 
  • The iterators are executed in parallel. 
  • The results of the transform are in the final callback.

variations : 
  • async.mapSeries(array, iterator, callback);
  • async.mapLimit(array, limit, iterator, callback); 





async.eachLimit(array, limit, iterator, callback)



  • Same as async.each()  except for you can limit the number of *parallel executions. 

  • limit - The maximum number of iterators to run at any time.

async.filter(array, filter, callback)


  • Produces a new array of values which pass the truth test function (filter). 
  • Callback accepts a single argument true/false.
  • The results available as an array with the "values" which passed the test. 

async.detect(array, iterator, callback)  returns first value which passed the test
async.sortBy(array, iterator, callback)  returns sorted results
async.some(array, iterator, callback)  returns true if any element passes the test
async.every(array, iterator, callback)  returns true if all values  pass the test.
async.concat(array, iterator, callback) *concat the results



async.reject(array, filter, callback)


  • Produces a new array of values which fail the truth test function (filter). 
  • Callback accepts a single argument true/false.
  • The results available as an array with the "values" which failed the test. 

Control Flow functions.


series
waterfall
compose

async.series(tasks, callback)


  • Run an array of functions in series, each one running once the previous function has completed
 

  • Once the tasks have completed, the results are passed to the final callback as an array.
 
 
async.parallel(tasks, callback);
async.parallelLimit(tasks, limit callback);

async.waterfall(tasks, callback)



  • Runs an array of functions in series, each passing their results to the next in the array.
 
 

async.compose(fn1, fn2, fn3...)



  • Runs an array of functions in series, each passing their results to the next in the array.
 
 

Questions?



Async

By Amith Nambiar

Made with Slides.com

Async

An introduction to the async library

  • 3,634

More from Amith Nambiar