使用RxJS进行速率限制

Question

I'm discovering RxJS at the moment and one of my first tries was trying to achieve a rate limiting on API requests.

Somehow I am missing something and getting in the output just "undefined".

What am i doing wrong?

const Rx = require('rx');
const request = require('request');

function f() {
  return Rx.Observable.from(arguments);
}

function expand(condensedId) {
  console.log('requesting', condensedId)
  return f(request(INDEX_URL + '/' + condensedId));
}

const INDEX_URL = 'http://jsonplaceholder.typicode.com/posts';

var source = f([1,2,3,4,5,6,7])
  .windowWithTimeOrCount(5000, 2)//rate limitation, 2 every 5 seconds
  .flatMap(condensed => expand(condensed))
  .map(entry => entry.title);

var subscription = source.subscribe(
  function (x) {
    console.log('title: %s', x);
  },
  function (err) {
    console.log('Error: %s', err);
  },
  function () {
    console.log('Completed');
  });

Answer 1

Rx.Observable.from expects an iterable, and I don't think the response to request() is an iterable. You can pass a function that returns a Promise or an Observable to flatMap , and it will return a stream that will emit the data that's resolved.

Because of this, let's use request-promise instead of request and return a Promise in our expand function. Additionally, let's use the cheerio library to extract the html title:

const Rx = require('rx');
const request = require('request-promise');

// HTML parsing library
const cheerio = require('cheerio');

function f() {
  return Rx.Observable.from(arguments);
}

const INDEX_URL = 'http://jsonplaceholder.typicode.com/posts';

// Return an Observable of resolved responses
function expand(condensedId$) {
  return condensedId$.flatMap(id => request(INDEX_URL + '/' + id));
}

var source = f([1,2,3,4,5,6,7])
  .windowWithTimeOrCount(5000, 2)//rate limitation, 2 every 5 seconds
  .flatMap(condensed => expand(condensed))
  .map(body => {
    const $ = cheerio.load(body);
    return $('title').text();
   });