I have the code for my Promise.race() implementation, and it basically works. However, in this case:
promiseRace([Promise.reject('test_error'), Promise.resolve('test_value')])
I am getting test_value instead of test_error.
Why it happens?
const promiseRace = promises => new Promise((resolve, reject) => {
promises.forEach(p => {
if (
typeof p === 'object'
&& 'then' in p
&& typeof p.then === 'function'
) {
p.then(resolve).catch(reject);
} else {
resolve(p);
}
});
});
promiseRace([Promise.reject('test_error'),
Promise.resolve('test_value')]).then(value => { console.log(value); });This happens because in the following line, you call .catch on another (chained) promise, not on the original promise:
p.then(resolve).catch(reject);
Note how the then call does not get a reject callback argument, and so there is an extra -- intermediate asynchronous promise cycle. By the time the .catch callback is called (reject), the other case has already been dealt with (the fulfulled promise).
So change to:
p.then(resolve, reject);