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
ATL JS: Dive into RxJS Observables
Search
Jeremy Fairbank
November 27, 2017
Programming
2
280
ATL JS: Dive into RxJS Observables
Jeremy Fairbank
November 27, 2017
Tweet
Share
More Decks by Jeremy Fairbank
See All by Jeremy Fairbank
Connect.Tech 2020: Advanced Cypress Testing
jfairbank
1
190
CodeMash 2020: Solving the Boolean Identity Crisis
jfairbank
1
140
CodeMash 2020: Practical Functional Programming
jfairbank
1
310
Connect.Tech 2019: Practical Functional Programming
jfairbank
0
340
Connect.Tech 2019: Solving the Boolean Identity Crisis
jfairbank
0
170
Lambda Squared 2019: Solving the Boolean Identity Crisis
jfairbank
0
120
All Things Open 2018: Practical Functional Programming
jfairbank
2
260
Connect.Tech 2018: Effective React Testing
jfairbank
1
140
Fluent Conf 2018: Building web apps with Elm Tutorial
jfairbank
2
830
Other Decks in Programming
See All in Programming
Devin , 正しい付き合い方と使い方 / Living and Working with Devin
yukinagae
3
760
snacks.nvim内のセットアップ不要なプラグインを紹介 / introduce_snacks_nvim
uhooi
0
360
S3静的ホスティング+Next.js静的エクスポート で格安webアプリ構築
iharuoru
0
200
remix + cloudflare workers (DO) docker上でいい感じに開発する
yoshidatomoaki
0
120
AI Agents with JavaScript
slobodan
0
190
プログラミング教育のコスパの話
superkinoko
0
130
custom_lintで始めるチームルール管理
akaboshinit
0
180
PHPのガベージコレクションを深掘りしよう
rinchoku
0
260
SQL Server ベクトル検索
odashinsuke
0
130
自分のために作ったアプリが、グローバルに使われるまで / Indie App Development Lunch LT
pixyzehn
1
140
Coding Experience Cpp vs Csharp - meetup app osaka@9
harukasao
0
550
Agentic Applications with Symfony
el_stoffel
1
160
Featured
See All Featured
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
227
22k
Building an army of robots
kneath
304
45k
Build The Right Thing And Hit Your Dates
maggiecrowley
34
2.6k
Speed Design
sergeychernyshev
28
870
Measuring & Analyzing Core Web Vitals
bluesmoon
6
360
The World Runs on Bad Software
bkeepers
PRO
67
11k
Evolution of real-time – Irina Nazarova, EuRuKo, 2024
irinanazarova
7
620
Fontdeck: Realign not Redesign
paulrobertlloyd
83
5.5k
個人開発の失敗を避けるイケてる考え方 / tips for indie hackers
panda_program
102
19k
RailsConf 2023
tenderlove
29
1k
Side Projects
sachag
452
42k
Improving Core Web Vitals using Speculation Rules API
sergeychernyshev
12
630
Transcript
Dive into RxJS Jeremy Fairbank @elpapapollo / jfairbank Observables
Software is broken. We are here to fix it. Say
hi@testdouble.com
Async
Async API Callback
Callback fetchUserById(1, function(err, user) { if (err) { console.error('Could not
retrieve user'); } else { console.log(user); } });
}); }); }); }); }); }); Callback Callback Callback Callback
Callback Callback
function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if
(err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }
function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if
(err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }
function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if
(err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }
Async API ?
Promise function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer
=> customer.name); }
.then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...)
Error Error Error Error
function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer =>
customer.name) .catch(err => { logError(err); throw err; }); }
Getting there…
• More readable and maintainable async code • Better error
handling • More declarative and versatile syntax • Capable of handling events, streams, and HTTP
RxJS Observables
Arrays [ 1, 2, 3, 4, 5 ] Sequences in
space
Observables Sequences in time 1 2 3 4 5
Reactive
Reactive 3
import { Observable } from 'rxjs'; const source = Observable.of(1,
2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
import { Observable } from 'rxjs'; const source = Observable.of(1,
2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
import { Observable } from 'rxjs'; const source = Observable.of(1,
2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
import { Observable } from 'rxjs'; const source = Observable.of(1,
2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 1
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 1
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 2
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 2
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 3
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 3
Declarative Transformation Operate on events
Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x =>
console.log(x)); // 2 // 4 // 6
Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x =>
console.log(x)); // 2 // 4 // 6
Observable.of(1, 2, 3) console.log n * 2 map subscribe
Observable.of(1, 2, 3) console.log n * 2 map subscribe 1
Observable.of(1, 2, 3) console.log n * 2 map subscribe 1
Observable.of(1, 2, 3) console.log n * 2 map subscribe 2
Observable.of(1, 2, 3) console.log n * 2 map subscribe 2
Observable.of(1, 2, 3) console.log n * 2 map subscribe
Observable.of(1, 2, 3) console.log n * 2 map subscribe 2
Observable.of(1, 2, 3) console.log n * 2 map subscribe 2
Observable.of(1, 2, 3) console.log n * 2 map subscribe 4
Observable.of(1, 2, 3) console.log n * 2 map subscribe 4
Observable.of(1, 2, 3) console.log n * 2 map subscribe
Observable.of(1, 2, 3) console.log n * 2 map subscribe 3
Observable.of(1, 2, 3) console.log n * 2 map subscribe 3
Observable.of(1, 2, 3) console.log n * 2 map subscribe 6
Observable.of(1, 2, 3) console.log n * 2 map subscribe 6
Lazy Transformation Do only as much work as needed
Observable.range(1, 100) .map(n => n * 2) .filter(n => n
> 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8
Observable.range(1, 100) .map(n => n * 2) .filter(n => n
> 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8
Observable.range(1, 100) .map(n => n * 2) .filter(n => n
> 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8
Observable.range(1, 100) .map(n => n * 2) .filter(n => n
> 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8
Observable.range(1, 100) .map(n => n * 2) .filter(n => n
> 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take
console.log n * 2 map subscribe n > 4 1
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 1
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 2
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 2
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 2
Observable.range(1, 100) filter 2 take ×
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take
console.log n * 2 map subscribe n > 4 2
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 2
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 4
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take 4
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take 4 ×
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take
console.log n * 2 map subscribe n > 4 3
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 3
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 6
Observable.range(1, 100) filter 2 take
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take 6
✓ console.log n * 2 map subscribe n > 4
Observable.range(1, 100) filter 2 take 6
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 2 take 6
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 1 take 6
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 1 take
console.log n * 2 map subscribe n > 4 4
Observable.range(1, 100) filter 1 take
console.log n * 2 map subscribe n > 4 4
Observable.range(1, 100) filter 1 take
console.log n * 2 map subscribe n > 4 8
Observable.range(1, 100) filter 1 take
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 1 take 8
✓ console.log n * 2 map subscribe n > 4
Observable.range(1, 100) filter 1 take 8
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 1 take 8
console.log n * 2 map subscribe n > 4 Observable.range(1,
100) filter 0 take 8
DOM Events
let counter = 0; function updateCounter(n) { counter += n;
counterEl.innerHTML = counter; } incrementBtn.addEventListener('click', () => { updateCounter(1); }); decrementBtn.addEventListener('click', () => { updateCounter(-1); });
let counter = 0; function updateCounter(n) { counter += n;
counterEl.innerHTML = counter; } incrementBtn.addEventListener('click', () => { updateCounter(1); }); decrementBtn.addEventListener('click', () => { updateCounter(-1); });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0)
.subscribe((counter) => { counterEl.innerHTML = counter; });
.scan((acc, curr) => acc + curr, 0)
.scan((acc, curr) => acc + curr, 0) Accumulated counter value
.scan((acc, curr) => acc + curr, 0) Current event value
(1)
.scan((acc, curr) => acc + curr, 0) Return new accumulated
counter value
.scan((acc, curr) => acc + curr, 0) Initial counter value
counterEl.innerHTML = counter acc + curr 1 mapTo subscribe 0
scan
acc + curr 1 mapTo subscribe e scan 0 counterEl.innerHTML
= counter
1 mapTo subscribe e scan acc + curr 0 counterEl.innerHTML
= counter
1 mapTo subscribe 1 scan acc + curr 0 counterEl.innerHTML
= counter
1 mapTo subscribe scan 1 acc + curr 0 counterEl.innerHTML
= counter
1 mapTo subscribe scan 1 acc + curr 1 Counter
value counterEl.innerHTML = counter
1 mapTo subscribe scan 1 acc + curr 1 counterEl.innerHTML
= counter
acc + curr 1 mapTo subscribe scan 1 counterEl.innerHTML =
counter
acc + curr 1 mapTo subscribe e scan 1 counterEl.innerHTML
= counter
1 mapTo subscribe e scan acc + curr 1 counterEl.innerHTML
= counter
1 mapTo subscribe 1 scan acc + curr 1 counterEl.innerHTML
= counter
1 mapTo subscribe scan 1 acc + curr 1 counterEl.innerHTML
= counter
1 mapTo subscribe scan 2 acc + curr 2 Counter
value counterEl.innerHTML = counter
1 mapTo subscribe scan 2 acc + curr 2 counterEl.innerHTML
= counter
const source = Observable.merge( Observable.fromEvent(incrementBtn, 'click').mapTo(1), Observable.fromEvent(decrementBtn, 'click').mapTo(-1), ); source
.scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });
const source = Observable.merge( Observable.fromEvent(incrementBtn, 'click').mapTo(1), Observable.fromEvent(decrementBtn, 'click').mapTo(-1), ); source
.scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });
const source = Observable.merge( Observable.fromEvent(incrementBtn, 'click').mapTo(1), Observable.fromEvent(decrementBtn, 'click').mapTo(-1), ); source
.scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });
const source = Observable.merge( Observable.fromEvent(incrementBtn, 'click').mapTo(1), Observable.fromEvent(decrementBtn, 'click').mapTo(-1), ); source
.scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });
const source = Observable.merge( Observable.fromEvent(incrementBtn, 'click').mapTo(1), Observable.fromEvent(decrementBtn, 'click').mapTo(-1), ); source
.scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement e counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement e counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement 1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement 1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement 1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement 1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement e counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement e counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement -1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 1 scan -1 mapTo
Increment Decrement -1 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement 0 counterEl.innerHTML = counter
acc + curr 1 mapTo subscribe 0 scan -1 mapTo
Increment Decrement 0 counterEl.innerHTML = counter
Async HTTP
Promise fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); });
});
Promise fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); });
});
Observable fetchOrders() .subscribe((orders) => { orders.forEach((order) => { console.log(order); });
});
Why Observables?
Promise fetchOrders() .then(orders => orders.filter( order => order.customerName === 'Tucker'
)) .then(orders => orders.map(order => order.id)) .then((orderIds) => { orderIds.forEach(id => console.log(id)); });
Promise fetchOrders() .then(orders => orders.filter( order => order.customerName === 'Tucker'
)) .then(orders => orders.map(order => order.id)) .then((orderIds) => { orderIds.forEach(id => console.log(id)); });
Promise fetchOrders() .then(orders => orders.filter( order => order.customerName === 'Tucker'
)) .then(orders => orders.map(order => order.id)) .then((orderIds) => { orderIds.forEach(id => console.log(id)); });
Promise fetchOrders() .then(orders => orders.filter( order => order.customerName === 'Tucker'
)) .then(orders => orders.map(order => order.id)) .then((orderIds) => { orderIds.forEach(id => console.log(id)); });
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Observable
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Observable
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Observable
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Observable
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Observable
Cancellation
const promise = fetchOrders() .then((orders) => { orders.forEach((order) => {
console.log(order); }); }); promise.cancel(); Promise
const promise = fetchOrders() .then((orders) => { orders.forEach((order) => {
console.log(order); }); }); promise.cancel(); Promise
const promise = fetchOrders() .then((orders) => { orders.forEach((order) => {
console.log(order); }); }); promise.cancel(); Promise ×
const subscription = fetchOrders() .subscribe((orders) => { orders.forEach((order) => {
console.log(order); }); }); subscription.unsubscribe(); Observable
const subscription = fetchOrders() .subscribe((orders) => { orders.forEach((order) => {
console.log(order); }); }); subscription.unsubscribe(); Observable Cancel request
Lazy Subscriptions
const p1 = fetchOrders(); const p2 = fetchOrders(); const p3
= fetchOrders(); Promises
const p1 = fetchOrders(); const p2 = fetchOrders(); const p3
= fetchOrders(); Promises Immediate
Observables const o1 = fetchOrders(); const o2 = fetchOrders(); const
o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe();
Observables Lazy const o1 = fetchOrders(); const o2 = fetchOrders();
const o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe();
Observables Lazy const o1 = fetchOrders(); const o2 = fetchOrders();
const o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe(); Issue Request
const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe();
const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe(); Pure, shareable value
const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe(); Issue new request
with same observable Pure, shareable value
Create HTTP Requests
function fetchOrders() { return Observable.ajax.get('/orders'); } Built-in AJAX
function fetchOrders() { return Observable.ajax.get('/orders'); } Built-in AJAX
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation ?
Observable.of(1, 2, 3) .subscribe(x => console.log(x));
Observable.of(1, 2, 3) .subscribe(x => console.log(x)); Subscriber (or Observer)
Observable.of(1, 2, 3) .subscribe({ next: x => console.log(x), }); Subscriber
Object
Observable.of(1, 2, 3) .subscribe({ next: x => console.log(x), complete: ()
=> console.log('Done!'), }); // 1 // 2 // 3 // Done!
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });
Error Handling
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), error: e => console.error(e), }); // 1 // Error: Uh oh
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), error: e => console.error(e), }); // 1 // Error: Uh oh
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), error: e => console.error(e), }); // 1 // Error: Uh oh
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe(x => console.log(x)); No error handler, so what happens?
Error Error Error Error Promises
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe(x => console.log(x)); No swallowed errors!
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), error: e => console.error(e), }); // 1 // Error: Uh oh
const source = Observable.create((subscriber) => { subscriber.next(1); subscriber.error(new Error('Uh oh'));
subscriber.next(2); }); source.subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), error: e => console.error(e), }); // 1 // Error: Uh oh Never called
fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x =>
console.log(x)); Catching
fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x =>
console.log(x)); Catching
fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x =>
console.log(x)); Catching
fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x =>
console.log(x)); Catching
console.log catch subscribe fetchOrders() Observable.of([])
console.log catch subscribe fetchOrders() Observable.of([]) ✓
console.log catch subscribe fetchOrders() Observable.of([]) ✓
console.log catch subscribe fetchOrders() Observable.of([]) ×
console.log catch subscribe fetchOrders() Observable.of([]) ×
console.log catch subscribe fetchOrders() Observable.of([]) []
console.log catch subscribe fetchOrders() Observable.of([]) []
fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => {
logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => {
logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => {
logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => {
logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ✓
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ✓
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ✓
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ✓
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ×
console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × × []
Hot Cold vs.
Observable creates the source. Cold
Best for one-off unique requests. Cold
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); }
function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => {
subscriber.next(orders); subscriber.complete(); }); }); } Resource requested/created at subscription time
WebSockets
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }
const stream = ordersStream(); stream.subscribe(x => console.log(x));
subscriber .next(data) WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
subscriber .next(data) ... WebSocket Subscriber console.log stream.subscribe(x => console.log(x));
subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
None
.subscribe(...)
.subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)
.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)
Hot Observable closes over the source.
Hot Best for multicasting and sharing resources.
const url = 'ws://example.com/orders'; const socket = new WebSocket(url); function
ordersStream() { return Observable.create((subscriber) => { socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }
const url = 'ws://example.com/orders'; const socket = new WebSocket(url); function
ordersStream() { return Observable.create((subscriber) => { socket.addEventListener('message', (data) => { subscriber.next(data); }); }); } Resource created outside subscription
const url = 'ws://example.com/orders'; const socket = new WebSocket(url); function
ordersStream() { return Observable.create((subscriber) => { socket.addEventListener('message', (data) => { subscriber.next(data); }); }); } Close over existing resource when subscribing
const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x));
const sub2 = stream.subscribe(x => console.log(x));
Shared stream of data const stream = ordersStream(); const sub1
= stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));
subscriber .next(event.data) WebSocket Subscriber console.log stream.subscribe(x => console.log(x))
subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
subscriber .next(event.data) WebSocket Subscriber console.log New Subscriber console.log stream.subscribe(...) stream.subscribe(...)
subscriber .next(event.data) WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber New
Subscriber
subscriber .next(event.data) WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber New
Subscriber
subscriber .next(event.data) WebSocket console.log ... console.log ... stream.subscribe(...) stream.subscribe(...) Subscriber
New Subscriber
subscriber .next(event.data) ... WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber
New Subscriber
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }) .share(); } Share It
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }) .share(); } Share It
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }) .share(); } Share It
const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x));
const sub2 = stream.subscribe(x => console.log(x));
Shared stream of data too const stream = ordersStream(); const
sub1 = stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));
Clean Up
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); return () => { socket.close(); }; }) .share(); }
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); return () => { socket.close(); }; }) .share(); } Called when all subscriptions unsubscribe
function ordersStream() { return Observable.create((subscriber) => { const url =
'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); return () => { socket.close(); }; }) .share(); } Close socket, deallocate resources, etc.
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); Recall
fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order
=> order.id) .subscribe(id => console.log(id)); ? Recall
Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2,
3 ]
Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2,
3 ]
Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2,
3 ]
Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 //
2 // 3
Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 //
2 // 3 Flatten
Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 //
2 // 3
subscribe mergeAll console.log [1, 2, 3]
subscribe mergeAll console.log [1, 2, 3]
subscribe mergeAll console.log [2, 3] 1
subscribe mergeAll console.log [2, 3] 1
subscribe mergeAll console.log [3] 2
subscribe mergeAll console.log [3] 2
subscribe mergeAll console.log 3
subscribe mergeAll console.log 3
Higher Order Observables
Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x =>
console.log(x)); // 2 // 4 // 6
Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x =>
console.log(x)); // 2 // 4 // 6 Delay?
Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .subscribe(x =>
console.log(x)); // ScalarObservable { value: 2 } // ScalarObservable { value: 4 } // ScalarObservable { value: 6 }
Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .subscribe(x =>
console.log(x)); // ScalarObservable { value: 2 } // ScalarObservable { value: 4 } // ScalarObservable { value: 6 }
Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .subscribe(x =>
console.log(x)); // ScalarObservable { value: 2 } // ScalarObservable { value: 4 } // ScalarObservable { value: 6 }
Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .mergeAll() .subscribe(x
=> console.log(x)); // 2 // 4 // 6
Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .mergeAll() .subscribe(x
=> console.log(x)); // 2 // 4 // 6
Observable.of(1, 2, 3) .mergeMap(n => Observable.of(n * 2)) .subscribe(x =>
console.log(x)); // 2 // 4 // 6
subscribe mergeMap console.log Observable.of(n * 2)
subscribe mergeMap console.log Observable.of(n * 2) 1
subscribe mergeMap console.log Observable.of(n * 2) 1
subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2
subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2
subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2
Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // <tick> // 1
Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // <tick> // 1
Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // <tick> // 1
Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // <tick> // 1
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ))
.subscribe(x => console.log(x)); // <tick> // 2 // 4 // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ))
.subscribe(x => console.log(x)); // <tick> // 2 // 4 // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ))
.subscribe(x => console.log(x)); // <tick> // 2 // 4 // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ))
.subscribe(x => console.log(x)); // <tick> // 2 // 4 // 6 ?
Concurrency
subscribe mergeMap console.log Observable.of(n * 2)
subscribe mergeMap console.log Observable.of(n * 2) 1
subscribe mergeMap console.log Observable.of(n * 2) 1
subscribe mergeMap console.log Observable.of(n * 2) 2
subscribe mergeMap console.log Observable.of(n * 2) 2 2
subscribe mergeMap console.log Observable.of(n * 2) 2 2
subscribe mergeMap console.log Observable.of(n * 2) 2 4
subscribe mergeMap console.log Observable.of(n * 2) 3 2 4
subscribe mergeMap console.log Observable.of(n * 2) 3 2 4
subscribe mergeMap console.log Observable.of(n * 2) 2 4 6
subscribe mergeMap console.log Observable.of(n * 2) 2 4 6
subscribe mergeMap console.log Observable.of(n * 2) 4 6 2
subscribe mergeMap console.log Observable.of(n * 2) 6 4
subscribe mergeMap console.log Observable.of(n * 2) 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ),
1) .subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ),
1) .subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ),
1) .subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ),
1) .subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ),
1) .subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
Observable.of(1, 2, 3) .concatMap(n => ( Observable.of(n * 2).delay(1000) ))
.subscribe(x => console.log(x)); // <tick> // 2 // <tick> // 4 // <tick> // 6
subscribe concatMap console.log Observable.of(n * 2)
subscribe console.log Observable.of(n * 2) 1 concatMap
subscribe console.log Observable.of(n * 2) 1 concatMap
subscribe console.log Observable.of(n * 2) 2 concatMap
subscribe console.log Observable.of(n * 2) 2 concatMap
subscribe console.log Observable.of(n * 2) 2 concatMap
subscribe console.log Observable.of(n * 2) 2 concatMap
subscribe console.log Observable.of(n * 2) 2 concatMap
subscribe console.log Observable.of(n * 2) 4 concatMap
subscribe console.log Observable.of(n * 2) 4 concatMap
subscribe console.log Observable.of(n * 2) 4 concatMap
subscribe console.log Observable.of(n * 2) 3 concatMap
subscribe console.log Observable.of(n * 2) 3 concatMap
subscribe console.log Observable.of(n * 2) 6 concatMap
subscribe console.log Observable.of(n * 2) 6 concatMap
subscribe console.log Observable.of(n * 2) 6 concatMap
Rate Limiting
Observable.of(1, 2, 3) .concatMap((id) => { const url = `/orders/${id}`;
return Observable.ajax.get(url) .delay(1000); }) .pluck('response') .bufferCount(3) .subscribe(x => console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
Observable.of(1, 2, 3) .concatMap((id) => { const url = `/orders/${id}`;
return Observable.ajax.get(url) .delay(1000); }) .pluck('response') .bufferCount(3) .subscribe(x => console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
Observable.of(1, 2, 3) .concatMap((id) => { const url = `/orders/${id}`;
return Observable.ajax.get(url) .delay(1000); }) .pluck('response') .bufferCount(3) .subscribe(x => console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
Observable.of(1, 2, 3) .concatMap((id) => { const url = `/orders/${id}`;
return Observable.ajax.get(url) .delay(1000); }) .pluck('response') .bufferCount(3) .subscribe(x => console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
Observable .ajax .get(url) subscribe console.log pluck bufferCount 'response' 3 concatMap
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
1
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
R Rate limit next request
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
R
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
R
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3
O1
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 2
O1
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 2
O1 +
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 1
O1 O2
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 1
O1 O2 +
Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 0
O1 O2 O3
Observable .ajax .get(url) subscribe concatMap console.log […] pluck bufferCount 'response'
0
Sequential vs. Parallel
const promise = Promise.all([ fetchOrder(1), fetchOrder(2), fetchOrder(3), ]); promise.then(x =>
console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
const promise = Promise.all([ fetchOrder(1), fetchOrder(2), fetchOrder(3), ]); promise.then(x =>
console.log(x)); // [ { id: '1', name: 'Order 1' }, // { id: '2', name: 'Order 2' }, // { id: '3', name: 'Order 3' } ]
const source = Observable.forkJoin( fetchOrder(1), fetchOrder(2), fetchOrder(3) ); source.subscribe(x =>
console.log(x)); // [ { response: { id: 1, name: 'Order 1' } }, // { response: { id: 2, name: 'Order 2' } }, // { response: { id: 3, name: 'Order 3' } } ]
const source = Observable.forkJoin( fetchOrder(1), fetchOrder(2), fetchOrder(3) ); source.subscribe(x =>
console.log(x)); // [ { response: { id: 1, name: 'Order 1' } }, // { response: { id: 2, name: 'Order 2' } }, // { response: { id: 3, name: 'Order 3' } } ]
const source = Observable.forkJoin( fetchOrder(1), fetchOrder(2), fetchOrder(3) ); source.subscribe(x =>
console.log(x)); // [ { response: { id: 1, name: 'Order 1' } }, // { response: { id: 2, name: 'Order 2' } }, // { response: { id: 3, name: 'Order 3' } } ] Observable or Promise
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log R1
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 subscribe console.log
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 subscribe console.log R3
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R3 subscribe console.log
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R3 subscribe console.log R2
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R2 R3 subscribe console.log
fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log R1 R2 R3
Tip of the iceberg
• Declarative, lazy operations • Expressive event management • No
more error swallowing • Rate limiting and concurrent processing
• Declarative, lazy operations • Expressive event management • No
more error swallowing • Rate limiting and concurrent processing ✓ ✓ ✓ ✓
github.com/ReactiveX/rxjs reactivex.io/rxjs RxJS
Observables ECMAScript Proposal: github.com/tc39/proposal-observable Another spec implementation: github.com/zenparsing/zen-observable
Thanks! Jeremy Fairbank @elpapapollo / jfairbank Slides: bit.ly/rxjs-atl-js