How to .catch a Promise.reject
Make sure every call to a then() returns a value.
For e.g.
var url = 'https://www.google.co.in';
var options = {};
var resolves = Promise.resolve();
resolves.then(() => {
console.log('Resolved first promise');
var fetchPromise = fetch(url, options);
fetchPromise.then(() => {
console.log('Completed fetch');
});
})
.catch(error => {
console.log('Error', error);
});Notice the console shows an uncaught exception. However, if you returned the inner promise (or any other value, which ends up turning into a promise via resolve), you end up flattening the promise so exception bubble up.
var url = 'https://www.google.co.in';
var options = {};
var resolves = Promise.resolve();
resolves.then(() => {
console.log('Resolved first promise');
var fetchPromise = fetch(url, options);
return fetchPromise.then(() => {
console.log('Completed fetch');
});
})
.catch(error => {
console.log('Error', error);
});Notice the exception bubbles up to the outer promise. Hope this clears up things a little bit.
function test() {
return new Promise((resolve, reject) => {
return reject('rejected')
})
}
test().then(function() {
//here when you resolve
})
.catch(function(rej) {
//here when you reject the promise
console.log(rej);
});