Fault-tolerant Promise.all

We'd like to fetch multiple URLs in parallel.

Here's the code to do that:

let urls = [
  'https://api.github.com/users/iliakan',
  'https://api.github.com/users/remy',
  'https://api.github.com/users/jeresig'
];

Promise.all(urls.map(url => fetch(url)))
  // for each response show its status
  .then(responses => { // (*)
    for(let response of responses) {
      alert(`${response.url}: ${response.status}`);
    }
  });

The problem is that if any of requests fails, then Promise.all rejects with the error, and we lose the results of all the other requests.

That's not good.

Modify the code so that the array responses in the line (*) would include the response objects for successful fetches and error objects for failed ones.

For instance, if one of the URLs is bad, then it should be like:

let urls = [
  'https://api.github.com/users/iliakan',
  'https://api.github.com/users/remy',
  'http://no-such-url'
];

Promise.all(...) // your code to fetch URLs...
  // ...and pass fetch errors as members of the resulting array...
  .then(responses => {  
    // 3 urls => 3 array members
    alert(responses[0].status); // 200
    alert(responses[1].status); // 200
    alert(responses[2]); // TypeError: failed to fetch (text may vary)
  });

P.S. In this task you don't have to load the full response using response.text() or response.json(). Just handle fetch errors the right way.

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Fault-tolerant Promise.all

1.4 KiB

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