expand

expand<T, R>(
  project: (value: T, index: number) => any,
  concurrent: number = Number.POSITIVE_INFINITY,
  scheduler: SchedulerLike = undefined
): OperatorFunction<T, R>

import { interval, of } from 'rxjs';
import { expand, take } from 'rxjs/operators';

// 投射 2
const source = of(2);
const example = source.pipe(
  // 递归调用提供的函数
  expand(val => {
    // 2,3,4,5,6
    console.log(`Passed value: ${val}`);
    // 3,4,5,6
    return of(1 + val);
  }),
  // 用5次
  take(5)
);

example.subscribe(val => console.log(`RESULT: ${val}`));
// 输出:
// 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

GET /users/willin/repos

Link: <https://api.github.com/user/1890238/repos?page=2>; rel="next",
      <https://api.github.com/user/1890238/repos?page=3>; rel="last"

import { Observable } from 'rxjs';
import { ajax, AjaxResponse } from 'rxjs/ajax';
import { map } from 'rxjs/operators';

export function get(
  url: string
): Observable<{
  content: object[];
  next: string | null;
}> {
  return ajax.get(url).pipe(
    map(response => ({
      content: response.response,
      next: next(response)
    }))
  );
}

function next(response: AjaxResponse): string | null {
  let url: string | null = null;
  const link = response.xhr.getResponseHeader('Link');
  if (link) {
    const match = link.match(/<([^>]+)>;\s*rel="next"/);
    if (match) {
      [, url] = match;
    }
  }
  return url;
}

import { empty } from 'rxjs';
import { concatMap, expand } from 'rxjs/operators';
import { get } from './get';

const url = 'https://api.github.com/users/willin/repos';
const repos = get(url).pipe(
  expand(({ next }) => (next ? get(next) : empty())),
  concatMap(({ content }) => content)
);
repos.subscribe(repo => console.log(repo));