Internal Viadeo presentation about the usage of promises with nodeJS on data aggregation layer.

1. PROMISES & LIMBO

2. GOAL
Showcase promises on Limbo
Simple methodology w/ Promises

3. SUMMARY
NodeJS & event-loop
What's a promise
Advanced usage

4. NODEJS & EVENT-LOOP
What's a promise
Advanced usage

5. SINGLE-THREADED ?

6. main event-loop
stack / queue
automatic (safe) threads, e.g.:
fs threads
net threads
etc.

8. Live sample (loupe)

9. Everything runs in parallel
except your code sic.

10. FLOW CONTROL

11. stuffA(params, function(err, result){
if (err){
return handleError(err);
}
goAhead(results);
});
Callback (CPS)

12. stuff(params, function(err, result){
if (err){
return handleError(err);
}
otherStuff(params, function(err, result){
if (err){
return handleError(err);
}
yetAnotherStuff(params, function(err, result){
if (err){
return handleError(err);
}
goAhead(results);
});
});
});
The famous callback Hell

13. SUGAR PATTERNS
Event Emitters
Observers
Generators
library
Promises ...
Async

14. NodeJS & event-loop
WHAT'S A PROMISE
Advanced usage

15. PROMISES IN JS
Not in the language
Soon to be with ES6 (iojs, node —-harmony)
Close-to-spec modulebluebird

16. A promise represents the eventual result of
an asynchronous operation
Promises/A+ specification

17. STATES
pending -
fulfilled any value
rejected reason Object
A promise is resolved once.

18. WRITE A PROMISE
var promA = new Promise(function(resolve, reject){
// ... any async computation ...
reject(new Error('Arf')); // rejected ;_;
// ...
resolve(result); // fulfilled ^_^
});
// -> Promise object

19. COMBINATION
a promise is theanable
a promise chain returns a promise
var promC = promA.then(promB);
// -> returns a Promise object

20. HANDLING ERRORS/REJECTIONS
prom.then(onFulfilled, onRejected);
// Is equivalent to
prom.then(onFulfilled).catch(onRejected);

21. HANDLING ERRORS/REJECTIONS
var promC = promA.then(promB).catch(function handleError(err){
log(err);
});
even if promA or is rejected, promC will be fulfilled
var promC = promA.then(promB).catch(function handleError(err){
log(err);
throw err; // broadcast error
});
if promA is rejected, promC will be rejected

22. NodeJS & event-loop
What's a promise
ADVANCED USAGE

23. COLLECTIONS
Promise.all([promise1, promise2, ...]);
// -> returns a single promise
fulfilled when all promises are
rejected when one of the promises is

24. PROMISIFICATION
from CPS to promise style
var request = require('request');
Promise.promisifyAll(request);
// creates promises from cps async functions
request.get('url', options, function(err, result){
...
});
request.getAsync(url, options).then(...);
// -Async suffixed functions return promises

25. NODEIFICATION
from promise style to CPS
function getInfo(token, callback){
...
return infoFrom(token).nodeify(callback);
}
getInfo('h3dsxz4i');
// -> returns a promise
getInfo('h3dsxz4i', function(err, result){...});
// -> returns a promise too actually
Both signatures accepted

26. RESOLUTION PATTERN
put on your glasses plz

31. var
prom_A = stuff_A(params),
prom_C = stuff_C(params),
prom_B = Promise.join(prom_A, prom_C).spread(handleResults_B),
prom_D = Promise.join(prom_A, prom_B).spread(handleResults_D)
;
prom_D.then(handleResults);

33. var
prom_A = stuff_A(params),
prom_C = stuff_C(params).catch(function(err){
log(err);
return {};
}),
prom_B = Promise.join(prom_A, prom_C).spread(handleResults_B),
prom_D = Promise.join(prom_A, prom_B).spread(handleResults_D)
;
prom_D.then(handleResults);

35. var
prom_A = stuff_A(params).catch(function(err){
log(err);
return 'Default stuff';
}),
prom_C = stuff_C(params).catch(function(err){
log(err);
return {};
}),
prom_B = Promise.join(prom_A, prom_C).spread(handleResults_B),
prom_D = Promise.join(prom_A, prom_B).spread(handleResults_D)
;
prom_D.then(handleResults);

36. var
prom_A = stuff_A(params).catch(function(err){
log(err);
return 'Default stuff';
}),
prom_C = stuff_C(params).catch(function(err){
log(err);
return {};
}),
prom_B = Promise.join(prom_A, prom_C).spread(handleResults_B),
prom_D = Promise.join(prom_A, prom_B).spread(handleResults_D)
;
prom_D.then(handleResults).catch(handleError);

37. Example in webapp
( )RecruiterStatisticsService#getAllJobOffersStats
return Promise.all([
jobOffersStatsPromise,
jobOffersStatsPromise
.then(getJobOffersIds)
.then(function (jobOffersIds) {
if (jobOffersIds.length) {
return getJobOfferProlongations(jobOffersIds);
}
})
])
.spread(mergeJobOffersStats).nodeify(callback)
;

38. Q/A

39. THX.
src/
src/
src/
src/
src/
Understanding the nodeJS event loop
What the heck is the event loop anyway?
docs.libuv.org/en/latest
promisesaplus.com
github.com/petkaantonov/bluebird

40. BYE.