how to use .cancel() with bluebird - promise

Question

document API here http://bluebirdjs.com/docs/api/cancellation.html
i try it in my demo,but doesn't work
var Promise = require('bluebird');
var a = require('./a');
var b = require('./b');
var cancelPromise = Promise.resolve();
cancelPromise.cancel();
cancelPromise = a.fnA()
.then(function() {
return b.fnB();
})
.then(function() {
console.log('done');
})
.finally(function() {
if (cancelPromise.isCancelled()) {
console.log('canceled');
}
console.log('end');
});
so how to use this method?

Answer 1

To use .cancel(), first you need to turn cancellation ON and only then call function .cancel()
If your work with bluebird below 3, your code should look something like that:
var mainAction = a.fnA()
.cancellable() // => cancellation turned on
.then(function() {
return b.fnB();
})
.then(function() {
console.log('done');
})
.catch(function( err ){ // => 'Reason for cancel'
console.error(err);
})
.finally(function() {
console.log('end');
});
mainAction.cancel('Reason for cancel');
And if you work with bluebird 3 and above, the code should look like this:
var successfulFetch = false, mainAction = a.fnA()
.then(function() {
return b.fnB();
})
.then(function() {
console.log('done');
}).finally(function() {
if(!successfulFetch){
console.error('Reason for cancel');
}
console.log('end');
});
mainAction.cancel();
Also I suggest you to take a look at this post: Cancel a delayed Bluebird promise
which was really helpful for me, when I had a similar problem