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pattern is a way to do pattern matching in javascript that helps you do asynchronous iterations.

var insert_all = require('p')
  , _

// pretending we are doing an async call
function insert_element(data, callback) {
  setTimeout(function() { callback(null, data); }, 100);

insert_all([], _, function (cb) { cb(); });
insert_all(function (l,cb) {
  var elem = l.shift(); // head
  insert_element(elem, function(err, elem) {
    if(err) { return cb(err); }
    console.log(elem + ' inserted');
    insert_all(l, cb);

insert_all([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], function () { 

the first pattern in pattern sets the arity of the function to execute. if you then give it anything with those numbers of arguments it will assume it must be the function.

// first call sets arity #2
insert_all([], _, function (cb) { cb(); });
// _ is an undefined variable we declared on the top
// the same as passing undefined
// will match anything

the last thing to be registered should be the catch all

// same as insert_all(_, _, function ...
insert_all(function (l,cb) {

when pattern finds a invocation where arguments.length matches arity it runs the functions.

// two arguments, arity #2. lets run!
insert_all([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], function () { 

this is what you normally would do.



  1. install npm
  2. npm install p
  3. var p = require('p');


  1. minimize p.js
  2. load it into your webpage


there are samples in the samples directory. check them out.


if you are not familiar with haskell and you love your javascript object oriented code you better look away right now. this pretty much breaks everything you love and care about in javascript

pattern was made so i could learn some more javascript. it's slow, and certainly not web scale

this software does not obey laws, common best practices, or even common sense

it does everything that is wrong in javascript; or at least attempts to (suggestions are welcome)

i'll probably still use it anyway


  • point free programming note i'm just kidding.

check issues


everyone is welcome to contribute. patches, bug-fixes, new features

  1. create an issue so the community can comment on your idea
  2. fork pattern
  3. create a new branch git checkout -b feature_name
  4. create tests for the changes you made
  5. make sure you pass both existing and newly inserted tests
  6. commit your changes
  7. push to your branch git push origin feature_name
  8. create an pull request


(oO)--',- in caos


copyright 2012 nuno job (oO)--',--

licensed under the apache license, version 2.0 (the "license"); you may not use this file except in compliance with the license. you may obtain a copy of the license at

unless required by applicable law or agreed to in writing, software distributed under the license is distributed on an "as is" basis, without warranties or conditions of any kind, either express or implied. see the license for the specific language governing permissions and limitations under the license.

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