async generator example

async-generator-example.ts

// @ts-ignore
const fetch = require('node-fetch');

function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function* getBooksPaged({ q, pageSize, lastPageIndex }) {
  let currentIndex = 0;
  let isDone = false;

  while (currentIndex < lastPageIndex && !isDone) {
    const pageResults = await getBooksPage({
      q,
      startIndex: currentIndex,
      maxResults: pageSize,
    });

    yield pageResults;

    if (pageResults.length < pageSize) {
      isDone = true;
    } else {
      currentIndex++;
    }
  }
}

async function getBooksPage({ q, startIndex, maxResults }) {
  const params = new URLSearchParams({ q, startIndex, maxResults });
  const response = await fetch(`https://www.googleapis.com/books/v1/volumes?${params.toString()}`);
  const jsonResponse = await response.json();
  const mapEssentialInfo = ({ volumeInfo }) => ({ title: volumeInfo.title });
  if(jsonResponse && jsonResponse.items) {
    return jsonResponse.items.map(mapEssentialInfo);
  } else {
    throw new Error('no items')
  }

}

(async  () => {
  const pages = getBooksPaged({ q: 'bitcoin', pageSize: 3, lastPageIndex: 5  });
  console.log('1')
  console.log('Searching books about bitcoin...');
  for await (const page of pages) {
    console.log('Page Results : ');
    console.log(page); // e.g. [ { title: 'Bitcoin: Introducción simple' }, { title: 'Bitcoin' }, { title: 'Bitcoins' } ]
    await delay(1000);
  }
})();