Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
JavaScript Promises - Thinking Sync in an Async...
Search
Kerrick Long
February 06, 2014
Programming
20
7.7k
JavaScript Promises - Thinking Sync in an Async World
Presented at the STL Ember.js Meetup on 2014-02-06. Video:
http://youtu.be/wc72cyYt8-c
Kerrick Long
February 06, 2014
Tweet
Share
More Decks by Kerrick Long
See All by Kerrick Long
15 Things You Shouldn't Do In Ember Anymore
kerrick
0
1.1k
The ECMAScript formerly known as 6
kerrick
0
1.3k
CSS Study Group 1
kerrick
0
1.2k
CSS Study Group 2
kerrick
1
1.1k
Services & Component Collaboration
kerrick
0
760
Donate STL #Build4STL Hackathon Keynote
kerrick
0
350
Donate STL
kerrick
0
810
TDD With Ember.js
kerrick
0
1.1k
Other Decks in Programming
See All in Programming
DataStoreをテストする
mkeeda
0
190
Go1.24 go vetとtestsアナライザ
kuro_kurorrr
2
700
本当だってば!俺もTRICK 2022に入賞してたんだってば!
jinroq
0
260
Productivity is Messing Around and Having Fun
hollycummins
0
140
RubyKaigiで手に入れた HHKB Studioのための HIDRawドライバ
iberianpig
0
1.1k
AIコードエディタの基盤となるLLMのFlutter性能評価
alquist4121
0
150
Go1.24で testing.B.Loopが爆誕
kuro_kurorrr
0
170
パスキーのすべて / 20250324 iddance Lesson.5
kuralab
0
140
Modern Angular:Renovation for Your Applications @angularDays 2025 Munich
manfredsteyer
PRO
0
150
プログラミング教育のコスパの話
superkinoko
0
120
いまさら聞けない生成AI入門: 「生成AIを高速キャッチアップ」
soh9834
13
3.9k
英語文法から学ぶ、クリーンな設計の秘訣
newnomad
1
270
Featured
See All Featured
Practical Tips for Bootstrapping Information Extraction Pipelines
honnibal
PRO
17
1.1k
Statistics for Hackers
jakevdp
798
220k
Keith and Marios Guide to Fast Websites
keithpitt
411
22k
StorybookのUI Testing Handbookを読んだ
zakiyama
28
5.6k
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
227
22k
How to Create Impact in a Changing Tech Landscape [PerfNow 2023]
tammyeverts
51
2.4k
Building Adaptive Systems
keathley
41
2.5k
The Illustrated Children's Guide to Kubernetes
chrisshort
48
49k
Why You Should Never Use an ORM
jnunemaker
PRO
55
9.3k
How to Ace a Technical Interview
jacobian
276
23k
VelocityConf: Rendering Performance Case Studies
addyosmani
328
24k
Cheating the UX When There Is Nothing More to Optimize - PixelPioneers
stephaniewalter
280
13k
Transcript
JavaScript Promises Thinking Sync in an Async World then
Kerrick Long Things I make and do Where to find
me online twitter.com/KerrickLong github.com/Kerrick Lead Front-end Developer! at Second Street KerrickLong.com www. meetup.com/STLEmber
try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally
{! logOut();! }!
try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally
{! logOut();! }! XMLHttpRequest
getStudent(name, function(student) {! getLatestGrade(student, function(grade) {! console.log(grade);! logOut();! });! });!
var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, function(error,
student) {! if (error) return handleError(error);! getLatestGrade(student, function(error, grade) {! if (error) return handleError(error);! console.log(grade);! logOut();! });! });!
var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, {!
error: handleError,! success: function(student) {! getLatestGrade(student, {! error: handleError! success: function(grade) {! console.log(grade);! logOut();! },! })! },! });!
try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally
{! logOut();! }! Awesome
var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, {!
error: handleError,! success: function(student) {! getLatestGrade(student, {! error: handleError! success: function(grade) {! console.log(grade);! logOut();! },! })! },! });! Awkward.
getStudent(name)! .then(getLatestGrade)! .then(console.log)! .catch(logError)! .then(logOut)! ;! Promises
None
Promise Basics
Promise Basics Consuming Promises
Promise Basics Consuming Promises Creating Promises
Promise Basics Consuming Promises Creating Promises Advanced Techniques
Promise Basics
Getting Promises
None
RSVP.js Q.js • Bluebird
RSVP.js Q.js • Bluebird Promises/A+
Promise Guarantees
Always Async
Always Async Returns a Promise
Always Async Returns a Promise Handled Once
Always Async Returns a Promise Handled Once Then’able
Promise States
Promise States Pending Fulfilled Rejected
Promise States Pending Fulfilled Rejected } Settled
Promise States Pending Fulfilled Rejected
Promise States Pending Fulfilled Rejected Value Reason
Promise States Pending Fulfilled Rejected Return Value Thrown Exception
Consuming Promises
Promise Prototype Methods
getJSON('/comments')! .then(onFulfilled, onRejected) Promise.prototype.then
getJSON('/comments')! .then(function(comments) {! if (comments) return 'Good'! else throw new
Error('Bad')! }, function(reason) {! // handle getJSON errors! }) Promise.prototype.then
getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then
getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then THROW
getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then THROW
getJSON onFulfilled onRejected getJSON onFulfilled onRejected
getJSON('/comments') // waiting...! .then(extractFirstId)! .then(getCommentById) // waiting...! .then(showComment) Promise.prototype.then
var promise = getJSON('/comments');! somethingElse();! promise.then(onFulfilled, onRejected); Promise.prototype.then
getJSON('/comments')! .then(null, onRejected) Promise.prototype.catch
getJSON('/comments')! .catch(onRejected) Promise.prototype.catch
Promise Static Methods
Promise.cast('Hi you!')! .then(onFulfilled, onRejected) Promise.cast
Promise.cast(seededRandom(42))! .then(onFulfilled, onRejected) Promise.cast
Promise.cast($.ajax(config))! .then(onFulfilled, onRejected) Promise.cast
$.ajax(config)! .then(onFulfilled, onRejected)
$.ajax(config)! .then(onFulfilled, onRejected) Lies, all LIES!
Promise.cast($.ajax(config))! .then(onFulfilled, onRejected) Promise.cast
var promises = [ getJSON('/a'),! getJSON('/b'), getJSON('/c') ]! ! Promise.all(promises)!
.then(allFulfilled, firstRejected) Promise.all
var promises = [ getJSON('/a'),! 'Hi you!', 42, getJSON('/c') ]!
! Promise.all(promises)! .then(allFulfilled, firstRejected) Promise.all
var promises = [ saveTo(server1),! saveTo(server2), saveTo(server3) ]! ! Promise.race(promises)!
.then(firstFulfilled, firstRejected) Promise.race
Creating Promises
new Promise()
function() {! var name = prompt('Your name?')! if (!name)! throw
new Error('Rude user!')! else! return name! } new Promise()
new Promise(function(fulfill, reject) {! var name = prompt('Your name?')! if
(!name)! throw new Error('Rude user!')! else! return name! }) new Promise()
new Promise(function(fulfill, reject) {! var name = prompt('Your name?')! if
(!name)! reject(new Error('Rude user!'))! else! fulfill(name)! }) new Promise()
Shortcuts
new Promise(function(fulfill, reject) {! fulfill(something)! }) Promise.resolve()
new Promise(function(fulfill, reject) {! fulfill(something)! })! Promise.resolve(something) Promise.resolve()
new Promise(function(fulfill, reject) {! reject(something)! }) Promise.reject()
new Promise(function(fulfill, reject) {! reject(something)! })! Promise.reject(something) Promise.reject()
Advanced Techniques
this.get('name') // 'Kerrick'! ! getJSON('/comments')! .then(function(comments) {! this.get('name') // throws!
}) this and bind()
this.get('name') // 'Kerrick'! var self = this! getJSON('/comments')! .then(function(comments) {!
self.get('name') // 'Kerrick'! }) this and bind()
this.get('name') // 'Kerrick'! ! getJSON('/comments')! .then(function(comments) {! this.get('name') // 'Kerrick'!
}.bind(this)) this and bind()
getJSON('/comments')! .then(function(comments) {! throw new Error('Hello?')! }) Absorbed Rejections
getJSON('/comments')! .then(function(comments) {! throw new Error('Hello?')! })! .catch(console.error.bind(console)) Absorbed Rejections
getStudent(name) // <Promise>! .then(getLatestGrade)! .then(log)! .catch(logError)! .then(logOut) Promise-aware Functions
log(getLatestGrade(getStudent(name)))! .catch(logError)! .then(logOut) Promise-aware Functions
function getLatestGrade(promise) {! return Promise.cast(promise)! .then(function(value) {! // getLatestGrade Logic!
})! } Promise-aware Functions