Discussion on: Javascript fetch, retry upon failure.

[YCM Jason]

Thanks for your comments! I am not sure if I understand your question correctly.

But it sounds like you are confused with the idea of "functions as first-class citizens", which is a fancy way of saying you can pass functions as a values around.

Are you familiar with setTimeout? Have a read about it here.

Consider

setTimeout(function() {
  print('hello')
}, 3000);

We are passing a function function () { print('hello'); } to setTimeout as the first argument. So if we call that function f, then we can equivilantly pass f to setTimeout.

const f = function () {
  print('hello');
}
setTimeout(f, 3000);

So in another words, my code:

.catch(function(error) {
  fetch_retry(url, options, n - 1)
    .then(resolve)
    .catch(reject);
})

Is basically equivalent to:

.catch(function(error) {
  fetch_retry(url, options, n - 1)
    .then(() => resolve())
    .catch(() => reject());
})

It is also important to note that the following is incorrect (or not the same):

.catch(function(error) {
  fetch_retry(url, options, n - 1)
    .then(resolve())
    .catch(reject());
})

Because Javascript will first evaluate resolve() and use the value it returns to pass on to then.

I hope I did help a little.