Promise 不等待函数 promise 被解析

Question

So I've been working on a scraper project.

Now I've implemented many things but I've been stuck on this one thing.

So first let me explain workflow: Scrapers are called in scraping-service module, where I wait for the promise of the functions called to be resolved. Data is fetched in scrapers, and passed to the data_functions object where data is: merged, validated and inserted into DB.

Now here is the code:

scraping-service

const olxScraper = require('./scrapers/olx-scraper');
const santScraper = require('./scrapers/sant-scraper');
//Calling scraper from where we want to get data about apartments
const data_functions = require('./data-functions/dataF');

let count = 1;

Promise.all([
  olxScraper.olxScraper(count),
  santScraper.santScraper(count),
]).then(() => data_functions.validateData(data_functions.mergedApartments));

So here I'm waiting for the promise of these two functions, and then passing merged data to validateData method in the data_functions .

Here is the scraper:

const axios = require('axios'); //npm package - promise based http client
const cheerio = require('cheerio'); //npm package - used for web-scraping in server-side implementations
const data_functions = require('../data-functions/dataF');

//olxScraper function which as paramater needs count which is sent in the scraping-service file.
exports.olxScraper = async (count) => {
  const url = `https://www.olx.ba/pretraga?vrsta=samoprodaja&kategorija=23&sort_order=desc&kanton=9&sacijenom=sacijenom&stranica=${count}`;
  //url where data is located at.
  const olxScrapedData = [];
  try {
    await load_url(url, olxScrapedData); //pasing the url and empty array
  } catch (error) {
    console.log(error);
  }
};

//Function that does loading URL part of the scraper, and starting of process for fetching raw data.
const load_url = async (url, olxScrapedData) => {
  await axios.get(url).then((response) => {
    const $ = cheerio.load(response.data);
    fetch_raw_html($).each((index, element) => {
      process_single_article($, index, element, olxScrapedData);
    });

    process_fetching_squaremeters(olxScrapedData); // if i place 
 //data_functions.mergeData(olxScrapedData); here it will work
  });
};

//Part where raw html data is fetched but in div that we want.
const fetch_raw_html = ($) => {
  return $('div[id="rezultatipretrage"] > div')
    .not('div[class="listitem artikal obicniArtikal  i index"]')
    .not('div[class="obicniArtikal"]');
};

//Here is all logic for getting data that we want, from the raw html.
const process_single_article = ($, index, element, olxScrapedData) => {
  $('span[class="prekrizenacijena"]').remove();
  const getLink = $(element).find('div[class="naslov"] > a').attr('href');
  const getDescription = $(element).find('div[class="naslov"] > a > p').text();
  const getPrice = $(element)
    .find('div[class="datum"] > span')
    .text()
    .replace(/\.| ?KM$/g, '')
    .replace(' ', '');
  const getPicture = $(element).find('div[class="slika"] > img').attr('src');
  //making array of objects with data that is scraped.
  olxScrapedData[index] = {
    id: getLink.substring(27, 35),
    link: getLink,
    description: getDescription,
    price: parseFloat(getPrice),
    picture: getPicture,
  };
};

//Square meters are needed to be fetched for every single article.
//This function loads up all links in the olxScrapedData array, and updating objects with square meters value for each apartment.
const process_fetching_squaremeters = (olxScrapedData) => {
  const fetchSquaremeters = Promise.all(
    olxScrapedData.map((item) => {
      return axios.get(item.link).then((response) => {
        const $ = cheerio.load(response.data);
        const getSquaremeters = $('div[class="df2  "]')
          .first()
          .text()
          .replace('m2', '')
          .replace(',', '.')
          .split('-')[0];
        item.squaremeters = Math.round(getSquaremeters);
        item.pricepersquaremeter = Math.round(
          parseFloat(item.price) / parseFloat(getSquaremeters)
        );
      });
    })
  );

  fetchSquaremeters.then(() => {
    data_functions.mergeData(olxScrapedData); //Sending final array to mergeData function.
    return olxScrapedData;
  });
};

Now if I console.log(olxScrapedData) in the fetchSquaremeters.then it will output scraped apartments, but it doesn't want to call the function data_functions.mergeData(olxScrapedData) . But if I add that block in the load_url , it will trigger the functions and data is being merged, but without square meters things, and I really need that data.

So my question is, how to make this work? Do I need to call function somewhere else or?

What I want is just that this last olxScrapedData be sent to this function mergeData so that my arrays from different scrapers would be merged into one.

Thanks!

Edit: also here is the other scrapers how it looks: https://jsfiddle.net/oh03mp8t/ . Note that in this scraper there is no any promises.

Answer 1

Try adding this: const process_fetching_squaremeters = async (olxScrapedData)... and then await fetchSquaremeters.then(..) .

James, in answer before told you what is happening. You must wait for this promise to be resolved, in order to all be executed correctly. If you don't have experience with async/await, promises, I suggest you watch some courses on them, to really understand what is happening here

Answer 2

Are you missing return/await statements from inside your promise/async statements, especially when your last statement is also a promise?

Without that, you may be simply asking the promise to be executed at a later time, rather than returning the result and making $.all() wait for it.