jimhigson/simple-barrier

A very minimalist, callback-based implementation of the Barrier flow control pattern in Javascript

simple-barrier

A very minimalist, callback-based implementation of the Barrier flow control pattern in Javascript. Happy in Node.js or the browser.

This is useful for when you want to wait for several things to execute in parallel, then handle the results together.

For people too lazy to learn async.

Installing

The usual.

npm install --save simple-barrier

Waiting for several async tasks

var simpleBarrier = require('simple-barrier'),
    fs = require('fs');

// create a barrier instance
var barrier = simpleBarrier();

// load some files, let the barrier handle the callbacks:
fs.readFile('foo.txt', barrier.waitOn());
fs.readFile('bar.txt', barrier.waitOn());
fs.readFile('baz.txt', barrier.waitOn());

// add a callback for when all files are loaded
barrier.endWith(function( results ){
   
   // Results is an array of the values given by fs.readFile
   // the array is in the order that barrier.waitOn() was called, regardless of the 
   // order they were loaded in
   console.log('foo, bar, and baz are:', results.join('\n'));
});

Actioning results one-by-one

// in this example we fetch two JSON files from the web,
// extracting just the part that we want:

var simpleBarrier = require('simple-barrier'),
    request = require('request');

var barrier = simpleBarrier();

function extractUsefulPart (err, data){
   // err, data are the standard arguments from request

   if( !err ){
      // the value we return will be added to the result array passed to the .endWith
      // callback. Here, we extract one small part of the whole JSON:
      return JSON.parse(data).usefulBit;
   }
   return null;
}

request('http://example.com/foo.json', barrier.waitOn( extractUsefulPart ));
request('http://example.com/baz.json', barrier.waitOn( extractUsefulPart ));

barrier.endWith(function( usefulBits ){
   usefulBits.forEach(function( bit ){
      console.log(bit + ' is useful');
   });
});

In the browser

Simple-barrier was written for node but it is happy in the browser as well:

var barrier = simpleBarrier();

// barrier expects the data to be the second argument (as per Node's errback convention)
// so we explicitly return the data param.
function useFirstArg(data){
    return data;
}

$.ajax({url:'people/steven.json'})
    .done(barrier.waitOn(useFirstArg));
    
$.ajax({url:'people/jim.json'})
    .done(barrier.waitOn(useFirstArg));

barrier.endWith(function( results ){
    console.log('all ajax requests returned', results);
});