create.md

create

signature: create(subscribe: function)

Create an observable with given subscription function.

Examples

Example 1: Observable that emits multiple values

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { Observable } from 'rxjs';
/*
  Create an observable that emits 'Hello' and 'World' on  
  subscription.
*/
const hello = Observable.create(function(observer) {
  observer.next('Hello');
  observer.next('World');
  observer.complete();
});

//output: 'Hello'...'World'
const subscribe = hello.subscribe(val => console.log(val));

Example 2: Observable that emits even numbers on timer

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { Observable } from 'rxjs';

/*
  Increment value every 1s, emit even numbers.
*/
const evenNumbers = Observable.create(function(observer) {
  let value = 0;
  const interval = setInterval(() => {
    if (value % 2 === 0) {
      observer.next(value);
    }
    value++;
  }, 1000);

  return () => clearInterval(interval);
});
//output: 0...2...4...6...8
const subscribe = evenNumbers.subscribe(val => console.log(val));
//unsubscribe after 10 seconds
setTimeout(() => {
  subscribe.unsubscribe();
}, 10000);

Additional Resources

• create 📰 - Official docs
• Creation operators: Create() 🎥 💵 - André Staltz
• Using Observable.create for fine-grained control 🎥 💵 - Shane Osbourne

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📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/observable/GenerateObservable.ts