Catching rejected fetch Promise

by Greg Pettit

HTML

<button onclick="stopper()">
Stop!
</button>

JavaScript

// this is just a placeholder. It will eventually be a function that evaluates.
let validContinue = true;
  
function shouldContinue() {
    return validContinue;
}
  
function stopper() {
    validContinue = false;
}

async function wonderPoll(someUrl) {

  // just a delay mechanism
  function wait(ms = 1000) {
    return new Promise(resolve => {
      setTimeout(resolve, ms);
    });
  }

  // the actual individual poll
  async function pollingFunction(url) {

    const response = await fetch(url, {
      cache: 'no-store'
    });

    if (response.ok) {
      return response;
    } else {
      Promise.reject(response);
    }

  }

  // allegedly keep polling until condition is met. But the rejected Promise is breaking out!
  while (shouldContinue()) {
    await wait();
    result = await pollingFunction(someUrl);
  }
  
  // when the fetch hits a rejected state, we never get here!
  console.log('done with the while loop, returning last successful result')

  return result;
}

const sampleUrl = 'https://get.geojs.io/v1/ip/country.json?ip=8.8.8.8';
const sampleUrl2 = 'http://totallybroken_fo_sho';

// swap the URL to test
wonderPoll(sampleUrl)
  .then((result) => {
    console.log('got a result', result)
  })
  .catch((err) => {
    console.log('got an error', err)
  });