en.javascript.info/6-async/04-promise-api/01-promise-errors-as-results/solution.md

The solution is actually pretty simple.

Take a look at this:

Promise.all(
  fetch('https://api.github.com/users/iliakan'),
  fetch('https://api.github.com/users/remy'),
  fetch('http://no-such-url')
)

Here we have an array of fetch(...) promises that goes to Promise.all.

We can't change the way Promise.all works: if it detects an error, then it rejects with it. So we need to prevent any error from occuring. Instead, if a fetch error happens, we need to treat it as a "normal" result.

Here's how:

Promise.all(
  fetch('https://api.github.com/users/iliakan').catch(err => err),
  fetch('https://api.github.com/users/remy').catch(err => err),
  fetch('http://no-such-url').catch(err => err)
)

In other words, the .catch takes an error for all of the promises and returns it normally. By the rules of how promises work, if a .then/catch handler returns a value (doesn't matter if it's an error object or something else), then the execution continues the "normal" flow.

So the .catch returns the error as a "normal" result into the outer Promise.all.

This code:

Promise.all(
  urls.map(url => fetch(url))
)

Can be rewritten as:

Promise.all(
  urls.map(url => fetch(url).catch(err => err))
)