1.
PROMISES/A+
WAS BORN
BOOM!

2.
HI, I’M @DOMENIC

3.
The JavaScript community’s
greatest strength
is that we turn tiny primitives into
powerful patterns.

4.
But it is also
our greatest weakness.

5.
The Promises/A+ story is a story wherein
the community overcame this weakness.

6.
Let’s talk about async.

7.
CONTINUATION PASSING STYLE
var fileName = "data.txt";
fs.readFile(fileName, function (err, data) {
// ...
});

8.
CPS is easy.
But it is not simple.

9.
CPS traps you in the Turing Tarpit.
return and throw, where did you go!

10.
ENTER PROMISES
 Joule and E’s promises
 Java’s java.util.concurrent.Future
 Python’s Twisted deferreds and PEP-3148 futures
 F#’s Async<T>
 .NET’s Task<T>
 C++11’s std::future
 Dart’s Future<T>
 JavaScript’s Promises/A+

11.
The point of promises is simple:
to give you back async versions of
return and throw.

12.
function* someNumbers() {
console.log("A");
yield 1;
console.log("B");
yield 2;
console.log("C");
yield 3;
console.log("D");
}
var iterator = someNumbers();
console.log(iterator.next()); // "A", { value: 1, done: false }
console.log(iterator.next()); // "B", { value: 2, done: false }
console.log(iterator.next()); // "C", { value: 3, done: false }
console.log(iterator.next()); // "D", { value: undefined, done: true }
http://jsbin.com/eqamor/1/edit

13.
Q.async(function* () {
$("#loading").text("Loading...").fadeIn();
try {
var repoEvents = yield getRepoEvents("kriskowal", "q");
updateUI(repoEvents);
$("#loading").text("Loaded!");
} catch (e) {
$("#loading").text("Error loading data: " + e.message);
} finally {
yield Q.delay(5000);
$("#loading").fadeOut();
}
})();
http://jsbin.com/igimow/1/edit

14.
As a bonus, we get time travel:
promises are objects representing
objects from a different time.
expect(promise).to.eventually.deep.equal(["zomg", "jsconf!"]);

15.
// ES5
userPromise
.get("repos").get(0)
.get("commitHistory")
.invoke("toHTML")
.then(displayInUI)
.done();
// ES6
const html = yield userPromise.repos[0].commitHistory.toHTML();
displayInUI(html);

16.
// ES5
userPromise
.get("repos").get(0)
.get("commitHistory")
.invoke("toHTML")
.then(displayInUI)
.done();
// ES6
const html = yield userPromise.repos[0].commitHistory.toHTML();
displayInUI(html);

17.
var Connection = require("q-connection");
var remote = Connection(port);
// a promise for the remote user object!
var userPromise = remote.invoke("getUser", "domenic");
 Web Socket
 Web Worker
 Message Port
https://github.com/kriskowal/q-connection/

18.
PROMISES IN JAVASCRIPT
The path to Promises/A+ has been
long and treacherous.

19.
It all started with CommonJS Promises/A
https://groups.google.com/d/msg/commonjs/6T9z75fohDk/U_0Gl9fPJxsJ

20.
Enter $.Deferred
http://bugs.jquery.com/ticket/11010

21.
Not Again!!
https://github.com/emberjs/ember.js/pull/1406
Horrible lies!

22.
https://gist.github.com/domenic/3889970

23.
https://github.com/domenic/promise-tests

24.
https://gist.github.com/briancavalier/eb5fc157825a170c9957

25.
http://promisesaplus.com

26.
ok, so what?

27.
https://github.com/promises-aplus/promises-spec/blob/master/implementations.md

28.
http://dom.spec.whatwg.org/#futures

29.
And if you don’t have an API you might
as well set up some Futures. Just in case.

30.
http://wiki.ecmascript.org/lib/exe/fetch.php?media=strawman:roadmap.pdf

31.
… what just happened?

32.
OPEN SPECIFICATION DEVELOPMENT
What made the Promises/A+ effort work so well?
 The cause
 The people
 The code
 The contract
 The setting

33.
the cause:
bringing sane asynchronicity to JS

34.
the people:
a strong and cooperative community

35.
the code:
existing convergent and widely-loved solutions

36.
the contract:
a small core for interoperation via standardization

37.
the setting:
GitHub

38.
An open standard for sound, interoperable JavaScript
promises—by implementers, for implementers.

39.
With these ingredients, you can extend the web forward.
http://yehudakatz.com/2013/05/21/extend-the-web-forward/

40.
THANKS!
promisesaplus.com
@promisesaplus