expand

signature: expand(project: function, concurrent: number, scheduler: Scheduler): Observable

Recursively call provided function.

Ultimate RxJS

Examples

Example 1: Add one for each invocation

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { interval, of } from 'rxjs';
import { expand, take } from 'rxjs/operators';
//emit 2
const source = of(2);
const example = source.pipe(
//recursively call supplied function
expand(val => {
//2,3,4,5,6
console.log(`Passed value: ${val}`);
//3,4,5,6
return of(1 + val);
}),
//call 5 times
take(5)
);
/*
"RESULT: 2"
"Passed value: 2"
"RESULT: 3"
"Passed value: 3"
"RESULT: 4"
"Passed value: 4"
"RESULT: 5"
"Passed value: 5"
"RESULT: 6"
"Passed value: 6"
*/
//output: 2,3,4,5,6
const subscribe = example.subscribe(val => console.log(`RESULT: ${val}`));

Additional Resources

  • expand 📰 - Official docs

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