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Syncing Async with Kyle Simpson Presented on September 17 2014 at FITC's Web Unleashed Toronto 2014 I bet you think “callback hell” is about function nesting and levels of indentation. Not so much. I bet you’ve heard that Promises replace callbacks. Nope. We need some clarity on what async flow control is all about in JavaScript. We’ll explore the perils of “Inversion of Control”, and see just what hell that leads us to. Then we’ll talk about promises as “continuation events” for function calls, and abstractions on top of promises that clean up our code. Finally, we’ll see how generators give us synchronous-looking async, and even how we can create cooperative concurrency with coroutines. Yield those confused async notions and control your flow. I promise we’ll get your thoughts in order. OBJECTIVE Learn why async flow control patterns are necessary for JS, why callbacks aren’t sufficient and how promises and generators are the solution. TARGET AUDIENCE JS developers ASSUMED AUDIENCE KNOWLEDGE Intermediate to advanced JS (3+ years experience). FIVE THINGS AUDIENCE MEMBERS WILL LEARN Why our brains reason about code differently than the JS engine does Why callback hell has much less to do with nesting/indentation than you thought What inversion of control is all about, and what trust issues it creates for our code What promises are and why they not only make code easier to reason about, but also solve inversion of control issues Why generators are even better, and how generators+promises are potentially the best pattern we can achieve thus far
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syncing asynckyle simpson
@getifyhttp://getify.me
to get started...
vs.
parallel
async
threads
event-loop concurrency
1234
123
1
2
34
1
23 done!
done!
async patterns
callbacks==
continuations
callbacksgot
problems2 major^
“callback hell”
still “callback hell”
inversion of control
trust:1. not too early2. not too late3. not too many times4. not too few times5. no lost context6. no swallowed errors...
nested callbacksare not
reasonable
we write
such syncmany steps
very wow
we think
js thinks
sync-looking async
synchronoussequentialblocking
hell is callbacks
-Sartre
promise: future value
promise: “completion” event
promises:1. only resolved once2. either success OR error3. messages passed/kept4. exceptions become errors5. immutable once resolved
uninversion of control
promise: flow control
scenario:load files in parallel, render in order, but ASAP
cool story, bro.
but...
scenario:timeout of a promise
blog.getify.com/promises-part-1/
github.com/getify/native-promise-only
promise abstractions
sequence=
series of automatically
chained promises
github.com/getify/asynquence
async + sequence =
asynquence
remember?load files in parallel, render in order, but ASAP
promises without all the fuss
gimme moar sync
ES6 generators
davidwalsh.name/es6-generators
generator + promises
yield promises
what about pre-ES6 browsers?
facebook.github.io/regenerator/
transpiledES5
“generators”
~ES7 async ?
github.com/lukehoban/ecmascript-asyncawait
CSP-likeconcurrency
.done()
chuckle, chuckle
thx!
kyle simpson@getify
http://getify.me
