CODEWITHSUNDEEP
javascriptecmascript-6es6-promise
user9623401
user9623401

Reputation:

(Javascript) why the catch doesn't catch the rejection?

Below is the promise chaining code:

new Promise(function(resolve, reject) {
  console.log('first');
  resolve('yes');
}).then(
  new Promise(function(resolve, reject) {
    console.log('second');
    reject('no');
  })
).catch(rej => console.log(rej));

And the output is :

'first'

'second'

I expected to get a 'no' output, but there wasn't. I don't know why the catch didn't catch the rejection from the second .then()?

Upvotes: 1

Views: 83

Answers (1)

CertainPerformance
CertainPerformance

Reputation: 370679

.then only accepts a function as a parameter - your

then(new Promise

is passing the second .then a Promise (that gets initialized *when the Promise chain is created, not when the prior Promise resolves). But .then doesn't know what to do when it's passed a Promise, it only deals with function parameters.

Instead, pass .then a function, and have that function create the Promise to be returned, and it will be properly caught:

new Promise(function(resolve, reject) {
  console.log('first');
  resolve('yes');
}).then(
  () => new Promise(function(resolve, reject) {
//^^^^^^
    console.log('second');
    reject('no');
  })
).catch(rej => console.log('catch: ' + rej));

Upvotes: 4

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