A promise is a promise

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JavaScript event synchronization and late subscription using Promises, with when.js

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1. A promise is a promise Synchronizing the asynchronous
2. David Iglesias Frontend Engineer at tuenti.com @ditman ditman@gmail.com
3. Async is rad! PSST: Event-oriented frameworks! Not just web servers!
4. Why is it cool? "Slow" calculations DON'T block the main flow in our application
5. How does it work? • Events ◦ "Things that happen" • Handlers / Callbacks ◦ They react to events
6. Tiny example class Balumba extends CarInsurance { - handleDone (price) { fire('done', Balumba, price); } + computePrice (carModel, age, gender) { BalumbaServer.on('done', handleDone); BalumbaServer.on('error', handleError); BalumbaServer.request(carModel, age, gender); } }
7. Tiny problem 1 Callbacks must be subscribed before the event gets fired!
8. Let's make our life harder class Rastreator { - providers = [ Balumba, Genesis, Verti, ... ]; - handleProviderDone(provider, price) {} + computePrice (carModel, age, gender) { foreach (providers as provider) { provider.on('done', handleProviderDone); provider.computePrice(carModel, age, gender); } // When all providers are done, show them } }
9. Tiny problem 2 Event synchronization™
11. No problemo! • Promises (AKA Future / Delay / Deferred) ◦ Proposed in 1976-77 ◦ Implemented in: ABCL/f, AmbientTalk, Io, Lucid, Oxygene, Oz, R, Scheme...
12. WTF? • Java ◦ java.util.concurrent.Future • C# ◦ await • JavaScript ◦ Promises/A, when.js, ...
13. Deferred (when.js) • Events "with memory" ◦ They "remember" being fired • Divided in 2 parts ◦ Promise (handles event subscriptions) ◦ Resolver (decides if the Promise gets resolved/rejected) • Synchronization ◦ all, any, some • Pipelining ◦ chain
14. Demo • Late subscription • Synchronization
15. To know more... Async JavaScript (Trevor Burnham) Coming (again) soon
16. Questions?