expand

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

Recursively call provided function.

expand - 图1

Examples

Example 1: Add one for each invocation

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  1. import { interval } from 'rxjs/observable/interval';
  2. import { of } from 'rxjs/observable/of';
  3. import { expand, take } from 'rxjs/operators';
  5. //emit 2
  6. const source = of(2);
  7. const example = source.pipe(
  8.   //recursively call supplied function
  9.   expand(val => {
  10.     //2,3,4,5,6
  11.     console.log(`Passed value: ${val}`);
  12.     //3,4,5,6
  13.     return of(1 + val);
  14.   }),
  15.   //call 5 times
  16.   take(5)
  17. );
  18. /*
  19.     "RESULT: 2"
  20.     "Passed value: 2"
  21.     "RESULT: 3"
  22.     "Passed value: 3"
  23.     "RESULT: 4"
  24.     "Passed value: 4"
  25.     "RESULT: 5"
  26.     "Passed value: 5"
  27.     "RESULT: 6"
  28.     "Passed value: 6"
  29. */
  30. //output: 2,3,4,5,6
  31. const subscribe = example.subscribe(val => console.log(`RESULT: ${val}`));

Additional Resources

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