expand

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

Recursively call provided function.

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}`));

Related Recipes

• Game Loop

Additional Resources

• expand - Official docs

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