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Dive into RxJS Jeremy Fairbank @elpapapollo / jfairbank Observables

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Software is broken. We are here to fix it. Say hi@testdouble.com

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Async

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Async API Callback

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Callback fetchUserById(1, function(err, user) { if (err) { console.error('Could not retrieve user'); } else { console.log(user); } });

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}); }); }); }); }); }); Callback Callback Callback Callback Callback Callback

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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); } } ); } }); }

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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); } } ); } }); }

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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); } } ); } }); }

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Async API ?

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Promise function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer => customer.name); }

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.then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...)

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Error Error Error Error

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function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer => customer.name) .catch(err => { logError(err); throw err; }); }

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Getting there…

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• More readable and maintainable async code • Better error handling • More declarative and versatile syntax • Capable of handling events, streams, and HTTP

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RxJS Observables

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Arrays [ 1, 2, 3, 4, 5 ] Sequences in space

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Observables Sequences in time 1 2 3 4 5

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Reactive

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Reactive 3

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const { Observable } = require('rxjs'); const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3

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const { Observable } = require('rxjs'); const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3

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const { Observable } = require('rxjs'); const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3

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const { Observable } = require('rxjs'); const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 1

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 1

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 2

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 2

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 3

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); console.log subscribe 3

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Declarative Transformation Operate on events

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Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x => console.log(x)); // 2 // 4 // 6

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Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x => console.log(x)); // 2 // 4 // 6

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Observable.of(1, 2, 3) console.log n * 2 map subscribe

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 1

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 1

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 2

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 2

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Observable.of(1, 2, 3) console.log n * 2 map subscribe

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 2

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 2

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 4

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 4

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Observable.of(1, 2, 3) console.log n * 2 map subscribe

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 3

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 3

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 6

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Observable.of(1, 2, 3) console.log n * 2 map subscribe 6

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Lazy Transformation Do only as much work as needed

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Observable.range(1, 100) .map(n => n * 2) .filter(n => n > 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8

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Observable.range(1, 100) .map(n => n * 2) .filter(n => n > 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8

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Observable.range(1, 100) .map(n => n * 2) .filter(n => n > 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8

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Observable.range(1, 100) .map(n => n * 2) .filter(n => n > 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8

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Observable.range(1, 100) .map(n => n * 2) .filter(n => n > 4) .take(2) .subscribe(x => console.log(x)); // 6 // 8

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 1 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 1 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 2 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 2 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 2 Observable.range(1, 100) filter 2 take ×

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 2 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 2 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 4 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take 4

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take 4 ×

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 3 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 3 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 6 Observable.range(1, 100) filter 2 take

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take 6

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✓ console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take 6

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 2 take 6

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 1 take 6

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 1 take

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console.log n * 2 map subscribe n > 4 4 Observable.range(1, 100) filter 1 take

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console.log n * 2 map subscribe n > 4 4 Observable.range(1, 100) filter 1 take

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console.log n * 2 map subscribe n > 4 8 Observable.range(1, 100) filter 1 take

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 1 take 8

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✓ console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 1 take 8

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 1 take 8

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console.log n * 2 map subscribe n > 4 Observable.range(1, 100) filter 0 take 8

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DOM Events

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let counter = 0; function updateCounter(n) { counter += n; counterEl.innerHTML = counter; } incrementBtn.addEventListener('click', () => { updateCounter(1); }); decrementBtn.addEventListener('click', () => { updateCounter(-1); });

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let counter = 0; function updateCounter(n) { counter += n; counterEl.innerHTML = counter; } incrementBtn.addEventListener('click', () => { updateCounter(1); }); decrementBtn.addEventListener('click', () => { updateCounter(-1); });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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Observable.fromEvent(incrementBtn, 'click') .mapTo(1) .scan((acc, curr) => acc + curr, 0) .subscribe((counter) => { counterEl.innerHTML = counter; });

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.scan((acc, curr) => acc + curr, 0) Accumulated counter value

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.scan((acc, curr) => acc + curr, 0) Current event value (1)

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.scan((acc, curr) => acc + curr, 0) Return new accumulated counter value

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.scan((acc, curr) => acc + curr, 0) Initial counter value

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counterEl.innerHTML = counter acc + curr 1 mapTo subscribe 0 scan

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acc + curr 1 mapTo subscribe e scan 0 counterEl.innerHTML = counter

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1 mapTo subscribe e scan acc + curr 0 counterEl.innerHTML = counter

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1 mapTo subscribe 1 scan acc + curr 0 counterEl.innerHTML = counter

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1 mapTo subscribe scan 1 acc + curr 0 counterEl.innerHTML = counter

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1 mapTo subscribe scan 1 acc + curr 1 Counter value counterEl.innerHTML = counter

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1 mapTo subscribe scan 1 acc + curr 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe scan 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe e scan 1 counterEl.innerHTML = counter

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1 mapTo subscribe e scan acc + curr 1 counterEl.innerHTML = counter

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1 mapTo subscribe 1 scan acc + curr 1 counterEl.innerHTML = counter

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1 mapTo subscribe scan 1 acc + curr 1 counterEl.innerHTML = counter

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1 mapTo subscribe scan 2 acc + curr 2 Counter value counterEl.innerHTML = counter

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1 mapTo subscribe scan 2 acc + curr 2 counterEl.innerHTML = counter

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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; });

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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; });

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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; });

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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; });

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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; });

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement e counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement e counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement 1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement e counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement e counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement -1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 1 scan -1 mapTo Increment Decrement -1 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement 0 counterEl.innerHTML = counter

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acc + curr 1 mapTo subscribe 0 scan -1 mapTo Increment Decrement 0 counterEl.innerHTML = counter

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Async HTTP

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Promise fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); }); });

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Promise fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); }); });

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Observable fetchOrders() .subscribe((orders) => { orders.forEach((order) => { console.log(order); }); });

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Why Observables?

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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)); });

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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)); });

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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)); });

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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)); });

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Observable

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Observable

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Observable

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Observable

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Observable

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Cancellation

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const promise = fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); }); }); promise.cancel(); Promise

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const promise = fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); }); }); promise.cancel(); Promise

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const promise = fetchOrders() .then((orders) => { orders.forEach((order) => { console.log(order); }); }); promise.cancel(); Promise ×

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const subscription = fetchOrders() .subscribe((orders) => { orders.forEach((order) => { console.log(order); }); }); subscription.unsubscribe(); Observable

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const subscription = fetchOrders() .subscribe((orders) => { orders.forEach((order) => { console.log(order); }); }); subscription.unsubscribe(); Observable Cancel request

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Lazy Subscriptions

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const p1 = fetchOrders(); const p2 = fetchOrders(); const p3 = fetchOrders(); Promises

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const p1 = fetchOrders(); const p2 = fetchOrders(); const p3 = fetchOrders(); Promises Immediate

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Observables const o1 = fetchOrders(); const o2 = fetchOrders(); const o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe();

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Observables Lazy const o1 = fetchOrders(); const o2 = fetchOrders(); const o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe();

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Observables Lazy const o1 = fetchOrders(); const o2 = fetchOrders(); const o3 = fetchOrders(); o1.subscribe(); o2.subscribe(); o3.subscribe(); Issue Request

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const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe();

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const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe(); Pure, shareable value

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const o1 = fetchOrders(); o1.subscribe(); o1.subscribe(); o1.subscribe(); Issue new request with same observable Pure, shareable value

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Create HTTP Requests

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function fetchOrders() { return Observable.ajax.get('/orders'); } Built-in AJAX

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function fetchOrders() { return Observable.ajax.get('/orders'); } Built-in AJAX

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Custom Observable Creation ?

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Observable.of(1, 2, 3) .subscribe(x => console.log(x));

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Observable.of(1, 2, 3) .subscribe(x => console.log(x)); Subscriber (or Observer)

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Observable.of(1, 2, 3) .subscribe({ next: x => console.log(x), }); Subscriber Object

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Observable.of(1, 2, 3) .subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), }); // 1 // 2 // 3 // Done!

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().mergeAll().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().mergeAll().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } fetchOrders().mergeAll().subscribe({ next: x => console.log(x), complete: () => console.log('Done!'), });

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Error Handling

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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

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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

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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

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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

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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?

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Error Error Error Error Promises

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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!

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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Catching

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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Catching

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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Catching

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ✓

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ✓

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ✓

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ✓

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([])

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × ×

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console.log catch subscribe legacyFetchOrders() fetchOrders() catch Observable.of([]) × × []

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Hot Cold vs.

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Observable creates the source Cold

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Best for one-off unique requests. Cold

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); }

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function fetchOrders() { return Observable.create((subscriber) => { fetchOrdersFromDb((orders) => { subscriber.next(orders); subscriber.complete(); }); }); } Resource requested/created at subscription time

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WebSockets

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function ordersStream() { return Observable.create((subscriber) => { const url = 'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }

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function ordersStream() { return Observable.create((subscriber) => { const url = 'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }

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function ordersStream() { return Observable.create((subscriber) => { const url = 'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }

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function ordersStream() { return Observable.create((subscriber) => { const url = 'ws://example.com/orders'; const socket = new WebSocket(url); socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }

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const stream = ordersStream(); stream.subscribe(x => console.log(x));

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subscriber .next(data) WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x));

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subscriber .next(data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x));

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subscriber .next(data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x));

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subscriber .next(data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x));

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subscriber .next(data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x));

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.subscribe(...)

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.subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)

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.subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...) .subscribe(...)

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Hot Observable closes over the source

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Hot Best for multicasting and sharing resources.

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const url = 'ws://example.com/orders'; const socket = new WebSocket(url); function ordersStream() { return Observable.create((subscriber) => { socket.addEventListener('message', (data) => { subscriber.next(data); }); }); }

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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

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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

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const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));

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Shared stream of data const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));

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subscriber .next(event.data) WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x))

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subscriber .next(event.data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x))

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subscriber .next(event.data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x))

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subscriber .next(event.data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x))

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subscriber .next(event.data) ... WebSocket Subscribed Observable console.log stream.subscribe(x => console.log(x))

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subscriber .next(event.data) WebSocket Subscribed Observable console.log New Subscribed Observable console.log stream.subscribe(...) stream.subscribe(...)

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subscriber .next(event.data) WebSocket Subscribed Observable console.log ... New Subscribed Observable console.log stream.subscribe(...) stream.subscribe(...)

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subscriber .next(event.data) WebSocket Subscribed Observable console.log ... New Subscribed Observable console.log stream.subscribe(...) stream.subscribe(...)

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subscriber .next(event.data) WebSocket Subscribed Observable console.log ... New Subscribed Observable console.log ... stream.subscribe(...) stream.subscribe(...)

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subscriber .next(event.data) ... WebSocket Subscribed Observable console.log ... New Subscribed Observable console.log stream.subscribe(...) stream.subscribe(...)

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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

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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

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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

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const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));

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Shared stream of data too const stream = ordersStream(); const sub1 = stream.subscribe(x => console.log(x)); const sub2 = stream.subscribe(x => console.log(x));

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Clean Up

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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(); }

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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

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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.

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); Recall

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fetchOrders() .mergeAll() .filter( order => order.customerName === 'Tucker' ) .map(order => order.id) .subscribe(id => console.log(id)); ? Recall

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Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2, 3 ]

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Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2, 3 ]

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Observable.of([1, 2, 3]) .subscribe(x => console.log(x)); // [ 1, 2, 3 ]

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Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 // 2 // 3

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Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 // 2 // 3 Flatten

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Observable.of([1, 2, 3]) .mergeAll() .subscribe(x => console.log(x)); // 1 // 2 // 3

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subscribe mergeAll console.log [1, 2, 3]

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subscribe mergeAll console.log [1, 2, 3]

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subscribe mergeAll console.log [2, 3] 1

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subscribe mergeAll console.log [2, 3] 1

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subscribe mergeAll console.log [3] 2

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subscribe mergeAll console.log [3] 2

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subscribe mergeAll console.log 3

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subscribe mergeAll console.log 3

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Higher Order Observables

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Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x => console.log(x)); // 2 // 4 // 6

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Observable.of(1, 2, 3) .map(n => n * 2) .subscribe(x => console.log(x)); // 2 // 4 // 6 Delay?

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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 }

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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 }

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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 }

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Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .mergeAll() .subscribe(x => console.log(x)); // 2 // 4 // 6

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Observable.of(1, 2, 3) .map(n => Observable.of(n * 2)) .mergeAll() .subscribe(x => console.log(x)); // 2 // 4 // 6

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Observable.of(1, 2, 3) .mergeMap(n => Observable.of(n * 2)) .subscribe(x => console.log(x)); // 2 // 4 // 6

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subscribe mergeMap console.log Observable.of(n * 2)

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subscribe mergeMap console.log Observable.of(n * 2) 1

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subscribe mergeMap console.log Observable.of(n * 2) 1

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subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2

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subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2

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subscribe mergeMap console.log Observable.of(n * 2) Observable.of(2) subscribe 2

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Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // // 1

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Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // // 1

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Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // // 1

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Observable.of(1) .delay(1000) .subscribe(x => console.log(x)) // // 1

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) )) .subscribe(x => console.log(x)); // // 2 // 4 // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) )) .subscribe(x => console.log(x)); // // 2 // 4 // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) )) .subscribe(x => console.log(x)); // // 2 // 4 // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) )) .subscribe(x => console.log(x)); // // 2 // 4 // 6 ?

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Concurrency

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subscribe mergeMap console.log Observable.of(n * 2)

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subscribe mergeMap console.log Observable.of(n * 2) 1

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subscribe mergeMap console.log Observable.of(n * 2) 1

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subscribe mergeMap console.log Observable.of(n * 2) 2

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subscribe mergeMap console.log Observable.of(n * 2) 2 2

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subscribe mergeMap console.log Observable.of(n * 2) 2 2

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subscribe mergeMap console.log Observable.of(n * 2) 2 4

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subscribe mergeMap console.log Observable.of(n * 2) 3 2 4

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subscribe mergeMap console.log Observable.of(n * 2) 3 2 4

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subscribe mergeMap console.log Observable.of(n * 2) 2 4 6

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subscribe mergeMap console.log Observable.of(n * 2) 2 4 6

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subscribe mergeMap console.log Observable.of(n * 2) 4 6 2

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subscribe mergeMap console.log Observable.of(n * 2) 6 4

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subscribe mergeMap console.log Observable.of(n * 2) 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ), 1) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ), 1) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ), 1) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ), 1) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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Observable.of(1, 2, 3) .mergeMap(n => ( Observable.of(n * 2).delay(1000) ), 1) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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Observable.of(1, 2, 3) .concatMap(n => ( Observable.of(n * 2).delay(1000) )) .subscribe(x => console.log(x)); // // 2 // // 4 // // 6

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subscribe concatMap console.log Observable.of(n * 2)

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subscribe console.log Observable.of(n * 2) 1 concatMap

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subscribe console.log Observable.of(n * 2) 1 concatMap

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subscribe console.log Observable.of(n * 2) 2 concatMap

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subscribe console.log Observable.of(n * 2) 2 concatMap

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subscribe console.log Observable.of(n * 2) 2 concatMap

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subscribe console.log Observable.of(n * 2) 2 concatMap

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subscribe console.log Observable.of(n * 2) 2 concatMap

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subscribe console.log Observable.of(n * 2) 4 concatMap

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subscribe console.log Observable.of(n * 2) 4 concatMap

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subscribe console.log Observable.of(n * 2) 4 concatMap

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subscribe console.log Observable.of(n * 2) 3 concatMap

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subscribe console.log Observable.of(n * 2) 3 concatMap

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subscribe console.log Observable.of(n * 2) 6 concatMap

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subscribe console.log Observable.of(n * 2) 6 concatMap

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subscribe console.log Observable.of(n * 2) 6 concatMap

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Rate Limiting

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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' } ]

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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' } ]

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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' } ]

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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' } ]

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Observable .ajax .get(url) subscribe console.log pluck bufferCount 'response' 3 concatMap

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3 1

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3 R Rate limit next request

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3 R

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3 R

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 3 O1

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 2 O1

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 2 O1 +

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 1 O1 O2

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 1 O1 O2 +

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Observable .ajax .get(url) subscribe concatMap console.log pluck bufferCount 'response' 0 O1 O2 O3

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Observable .ajax .get(url) subscribe concatMap console.log […] pluck bufferCount 'response' 0

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Sequential vs. Parallel

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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' } ]

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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' } ]

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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' } } ]

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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' } } ]

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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

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log R1

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 subscribe console.log

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 subscribe console.log R3

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R3 subscribe console.log

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R3 subscribe console.log R2

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin R1 R2 R3 subscribe console.log

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fetchOrder(1) fetchOrder(2) fetchOrder(3) forkJoin subscribe console.log R1 R2 R3

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Tip of the iceberg

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• Declarative, lazy operations • Expressive event management • No more error swallowing • Rate limiting and concurrent processing

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• Declarative, lazy operations • Expressive event management • No more error swallowing • Rate limiting and concurrent processing ✓ ✓ ✓ ✓

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github.com/ReactiveX/rxjs reactivex.io/rxjs RxJS

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Observables ECMAScript Proposal:
 github.com/tc39/proposal-observable Another spec implementation:
 github.com/zenparsing/zen-observable

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Thanks! Jeremy Fairbank @elpapapollo / jfairbank Slides: bit.ly/rxjs-connect