promises-chain v2

by Roman Fedytskyi

JavaScript

const urls = new Array(10).fill('').map((item, i) => `https://jsonplaceholder.typicode.com/posts/${++i}`);

    /* Solutions via reduce */
    const makeRequestsChain = () => {
      urls.reduce((accum, item) =>
        accum.then(() => fetch(item)), Promise.resolve());
    };

    /* Solutions via reduce with delay */
    const makeRequestsChainWithDelay = (delay = 3000) => {
      urls.reduce((accum, item) =>
        accum.then(() => new Promise(resolve => {
          setTimeout(() => {
            fetch(item);
            resolve();
          }, delay);
        })), Promise.resolve());
    };

    /* Solutions via reduce with passing arguments */
    const makeRequestsChainWithPassingArguments = () => {
      const getJson = data => data.json();
      // TODO: this log function exists only for presentation. It shows ability to put data from the prev request to the next one
      const log = data => console.error('data', data);
      const initState = Promise.resolve(new Response(JSON.stringify({})));

      urls.reduce((accum, item) =>
        accum
          .then(getJson)
          .then(log)
          .then(fetch.bind(null, item)), initState)
      .then(getJson)
      .then(log)
    };

    /* Solution via recursion*/
    const makeRequestsChainViaReqursion = () => {
      const makeRequests = urls => {
        const url = urls.shift();
        if (url) {
          fetch(url).then(() => makeRequests(urls))
        }
      };

      makeRequests(urls);
    };

    /* Solution via async/await */
    function chainPromisesViaAsync() {
      const promises = urls.map(async url => {
        const result = await fetch(url);
        return result;
      });

      Promise.all(promises).then(data => {
        console.error('data', data);
      });
    }