Asynchronous Promises (Fluent 2014)

Kris Kowal's presentation about asynchronous programming with Promises from O'Reilly's Fluent conference in 2014.

Transcript

1. Asynchronous Promises Kris Kowal Open Sourcerer @kriskowal montagestudio.com @montagejs ✉ ! kris@montagestudio.com O’Reilly Fluent 2014-03-13
2. var FS = require("fs");! var readJsonSync = function (path) {! var text = FS.readSync(path, "utf-8");! return JSON.parse(text);! }; synchronous
3. var FS = require("q-io/fs");! var readJsonPromise = Q.async(function *(path) {! var text = yield FS.read(path);! return JSON.parse(text);! }); asynchronous—promises and generators
4. var FS = require("q-io/fs");! function readJsonPromise(path) {! return FS.read(path)! .then(JSON.parse);! } asynchronous—promises
5. var FS = require("fs");! var readJsonWithNodebacks = function (path, nodeback) {! FS.readFile(path, "utf-8", function (error, content) {! var result;! if (error) {! return nodeback(error);! }! try {! result = JSON.parse(result);! } catch (error) {! return nodeback(error);! }! nodeback(null, result);! });! } nodeback
6. WHAT IS A PROMISE A promise is a proxy for a value from another time or place. The promise interface allows us to interact with that value consistently, regardless of whether the value comes from the past or the future, whether that value is near by or far away, or even if the value is demonstrably unavailable.
8. var Q = require("q");! var deferred = Q.defer();! // ... deferred.resolve()! deferred.promise! .then(console.log)! .done(); new Promise(function (resolve, reject) {! // ... resolve()
 })! .then(console.log)! .done(); As with Q ES6 Parlance
12. var outputPromise = inputPromise! .then(function (inputValue) {! return outputValue;! // or! throw outputError;! // or! return outputPromise;! }, function (inputError) {! return outputValue;! // or! throw outputError;! // or! return outputPromise;! });
14. return getUsername()! .then(function (username) {! return getUser(username);! })! // chained because we will not need the! // user name in the next event! .then(function (user) {! return getPassword()! // nested because we need both user and! // password next! .then(function (password) {! if (user.passwordHash !== hash(password)) {! throw new Error("Can't authenticate");! }! });! });
15. function retry(f, ms, times) {! return Q().then(f)! .then(null, function (error) {! if (times > 0) {! return Q()! .delay(ms)! .then(function () {! return retry(f, ms * 2, times - 1);! });! }! });! }
16. THE POINT OF PROMISES • implicit exception propagation • control flow correspondence • decoupling space and time • pipelined message passing • a debugging primitive • object capability programming • …
17. chatty protocol
18. pipelined messages
19. var Connection = require("q-connection");! var WebSocketServer = require("ws").Server;! var wss = new WebSocketServer({port: 8888});! wss.on("connection", function(ws) {! var local = {! greet: function (message) {! console.log("Greeting:", message);! }! };! Connection(ws, local);! }); server
20. client var Connection = require("q-connection");! var socket = new WebSocket("ws://localhost:8888");! var remote = Connection(socket);! remote.invoke("greet", "Hello, World!")! .done();
21. remote.get("v1").get("fs")! .invoke("read", "/etc/passwd")! .invoke("toUpperCase")! .done();
22. ASK ME ABOUT • Indefinite Promise Queues • Semaphores • Asynchronous Iterators • Generators • Promise Streams • Back Pressure • Limiting Parallelism • State Machines • Streaming Parsers • Reactive Bindings
23. PROMISES AND MONTAGE
24. var Q = require("q");! ! var id = 0;! ! exports.request = function (url, key) {! var deferred = Q.defer();! var script = document.createElement("script");! var callbackName = "resolveJsonp" + id++;! var join = url.indexOf("?") < 0 ? "?" : "&";! script.src = url + join + key + "=" + callbackName;! window[callbackName] = function (result) {! deferred.resolve(result);! delete window[callbackName];! };! document.head.appendChild(script);! return deferred.promise;! };
25. this.catImagesPromise = Jsonp.request(! "http://www.reddit.com/r/" + selectedSub + ".json?limit=100",! "jsonp"! )! .then(function (jsonData) {! var catImages = [];! for (var i = 0; i < jsonData.data.children.length; i++) {! var item = jsonData.data.children[i];! if (! item.data.url.toLowerCase()! .match(/i.imgur.com\/[a-zA-Z0-9]+.(jpg|gif)/)! ) {! catImages.push(item.data.url.replace(".jpg", "m.jpg"));! }! }! return catImages;! })! .delay(1000);
26. <div data-montage-id="substitution">! <div data-arg="pending">! <div data-montage-id="progress"></div>! </div>! <div data-arg="fulfilled">! <div data-montage-id="flow"></div>! </div>! </div>
29. Asynchronous Promises Kris Kowal Open Sourcerer @kriskowal montagestudio.com @montagejs ✉ ! kris@montagestudio.com O’Reilly Fluent 2014-03-13