JSFoo 2012
It’s like kung fu with JavaScript and objects! All about building full size apps in JavaScript.
YP
Yuvi Panda
@yuvipanda
Escape from Callback Hell with Deferreds
Submitted Aug 19, 2012
Section:
Zen of JavaScript
Technical level:
Intermediate
Session type:
Tutorial
- To explain fundamentals of deferreds, using jQuery’s implementation for demonstration
- Show how hard-to-understand callback based code can be converted to clearer Deferreds based code
Outline
Tired of writing JS with so many nested callbacks that it looks like the Gaza Pyramid turned sideways? Thought you’ll never have to write synchronization code again but suddenly find yourself wanting to wait on 5 callbacks to return before you want to execute something? Hate having to add ugly boilerplate everywhere if you ever want to chain callbacks? Miss the return statement? Think your code looks ugly because it has way too many levels of indentation?
Start using Deferreds and fix all these! Deferreds are a way of managing callbacks that is painless, elegant and powerful. Using deferreds makes your code cleaner, easier to understand and less error prone. And free ponies too!
Requirements
Intermediate level of Javascript knowledge would be sufficient.
Speaker bio
Yuvi Panda is a 21 year old open source geek who chases shiny new things way too often. He wrote major parts of the Wikipedia Android/iOS app (JS/Phonegap), and the upcoming Wiki Loves Monument app (also JS/PhoneGap). He was yearning for a threaded model in Javascript until he found Deferreds. Amongst his hobbies is screaming ‘USE DEFERREDS!’ at anyone claiming to use Javascript. He’s currently a student at KCG College of Technology.
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Yuvi Panda
@yuvipanda Submitter
Deferreds basics, waiting on multiple deferreds, + transforming a few hairy callback hell snippets into deferred based ones wouldn't be enough?
Sunil Pai
@threepointone
I think it's just fine for half an hour, actually.
Aditya
@netroy
cool. :)
BTW, i didn't say it won't be enough. I just said it'd be a better talk if you do mention other control flow methods, so that the noobs don't walk out thinking the deferreds are holy grail for writing async code. I personally like callbacks sometimes, while caolan's async is awesome in certain cases.
Deferreds/Promises make great chainable APIs, but what if you had to do an asynchronous map, reduce or filter on an array of 5000 items ? creating 5000 deferred objects would work, but won't be a good idea.
I know I'm being a bit anal, but the talk is marked as Intermediate.
Cheers
Yuvi Panda
@yuvipanda Submitter
Ah, right. In that case, perhaps I should mark it as beginner. I'm unsure of the beginner-intermediate-advanced levels - it is possible that spending too much time telling people 'NO, it is not
intibutint i' has skewed my perspective.jaseem abid
Don't miss promises.
Aditya
@netroy
Cool.. but you might consider covering other control-flow methods for dealing with async code and comparing them to deferreds.
Deferreds alone for 30 minutes wouldn't make a good talk.
Trivia: Deferreds were introduced by Dojo back in 2006