I handle the error in my Promise by catch, but in Node.js (v10.11.0) console output I see the message: (node:7424) UnhandledPromiseRejectionWarning: Error: Oops...
Why does it happen?
// See browser console, not stack snippet console, to see uncaught error
const p = new Promise((resolve,reject) => { throw new Error('Oops..');});
p.then(()=> console.log('Then'));
p.catch(err => console.log(err.message)); // the error handling
console.log('The end');Also, I get the same result for such variant of p initializing:
const p = new Promise((resolve,reject) => { reject(new Error('Oops..'));});
This is my output:
The end
Oops..
(node:7492) UnhandledPromiseRejectionWarning: Error: Oops..
Whenever you call .then (or .catch) on an existing Promise, you have a new Promise. The error results from the Promise chain created by
p.then(()=> console.log('Then'));
not being caught anywhere.
Either chain the .catch onto the .then:
const p = new Promise((resolve, reject) => {
throw new Error('Oops..');
});
p
.then(() => console.log('Then'))
.catch(err => console.log(err.message));
console.log('The end');Note that when constructing a Promise, it's a good idea to always call reject explicitly when there's an error, to ensure that the consumer of that Promise can catch problems. For example, in the following code, the p will not be rejected, and will remain unresolved forever, because the error was thrown asynchronously:
const p = new Promise((resolve, reject) => {
setTimeout(() => {
throw new Error('Oops..');
});
})
p
.then(() => console.log('Then'))
.catch(err => console.log(err.message))
console.log('The end');Better to call reject:
const p = new Promise((resolve, reject) => {
setTimeout(() => {
reject('Oops..');
});
})
p
.then(() => console.log('Then'))
.catch(err => console.log(err))
console.log('The end');Collected from the Internet
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