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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
[email protected]
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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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import { Observable } from 'rxjs'; const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
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import { Observable } from 'rxjs'; const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
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import { Observable } from 'rxjs'; const source = Observable.of(1, 2, 3); source.subscribe(x => console.log(x)); // 1 // 2 // 3
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import { Observable } from '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)
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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().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().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().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(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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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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fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x => console.log(x)); Catching
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fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x => console.log(x)); Catching
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fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x => console.log(x)); Catching
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fetchOrders() .catch((e) => { logError(e); return Observable.of([]); }) .subscribe(x => console.log(x)); Catching
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console.log catch subscribe fetchOrders() Observable.of([])
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console.log catch subscribe fetchOrders() Observable.of([]) ✓
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console.log catch subscribe fetchOrders() Observable.of([]) ✓
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console.log catch subscribe fetchOrders() Observable.of([]) ×
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console.log catch subscribe fetchOrders() Observable.of([]) ×
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console.log catch subscribe fetchOrders() Observable.of([]) []
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console.log catch subscribe fetchOrders() Observable.of([]) []
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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
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fetchOrders() .catch((e) => { logError(e); return legacyFetchOrders() .catch((e2) => { logError(e2); return Observable.of([]); }) }) .subscribe(x => console.log(x)); Or delegate to legacy API…
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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 console.log stream.subscribe(x => console.log(x)); Subscriber
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subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
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subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
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subscriber .next(data) ... WebSocket Subscriber console.log stream.subscribe(x => console.log(x));
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subscriber .next(data) ... WebSocket console.log stream.subscribe(x => console.log(x)); Subscriber
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No content
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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 Subscriber console.log stream.subscribe(x => console.log(x))
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subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
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subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
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subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
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subscriber .next(event.data) ... WebSocket console.log stream.subscribe(x => console.log(x)) Subscriber
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subscriber .next(event.data) WebSocket Subscriber console.log New Subscriber console.log stream.subscribe(...) stream.subscribe(...)
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subscriber .next(event.data) WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber New Subscriber
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subscriber .next(event.data) WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber New Subscriber
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subscriber .next(event.data) WebSocket console.log ... console.log ... stream.subscribe(...) stream.subscribe(...) Subscriber New Subscriber
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subscriber .next(event.data) ... WebSocket console.log ... console.log stream.subscribe(...) stream.subscribe(...) Subscriber New Subscriber
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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-atl-js