Wait until all promises have completed even when some reject, with Promise.all

PromisAllWithFails.js

var a = ["sdfdf", "http://oooooolol"],
    handleNetErr = function(e) { return e };

Promise.all(fetch('sdfdsf').catch(handleNetErr), fetch('http://invalidurl').catch(handleNetErr))
    .then(function(sdf, invalid) {
        console.log(sdf, invalid) // [Response, TypeError]
    })
    .catch(function(err) {
        console.log(err);
    })

Promise.all(a.map(function(e) { 
    return fetch(e).catch(handleNetErr) 
})).then(function(e) { 
    console.log('then',e) // Outputs: 'then', [Response, TypeError]
}).catch(function(e) { 
    console.log('err',e) 
})

PromiseAllWithFails.es6.js

let a = new Promise((res, rej) => res('Resolved!')),
    b = new Promise((res, rej) => rej('Rejected!')),
    c = a.catch(e => { console.log('"a" failed.'); return e; }),
    d = b.catch(e => { console.log('"b" failed.'); return e; });

Promise.all([c, d])
  .then((first, second) => console.log('Then', first, second)) // Then ["Resolved!", "Rejected!"]
  .catch(err => console.log('Catch', err));

Promise.all([a.catch(e => e), b.catch(e => e)])
  .then((first, second) => console.log('Then', first, second)) // Then ["Resolved!", "Rejected!"]
  .catch(err => console.log('Catch', err));
  

Inspired from your examples, I created a small library https://www.npmjs.com/package/promise-all-always

Very nice. The one downside I see is that, since this forces all promises to resolve, we can't tell whether the output of the promise is an error string or an actual output. That is, not unless we return an object that has a field that tells us whether this output is a rejection or a normal output.

awesome!! Thanks lots

Instead of using Promise.all() , you can use Promise.allSettled().
Refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/allSettled