how to cancel promises with bluebird - promise

Question

I think I misunderstand how promise cancellation with bluebird works. I wrote a test that demonstrates this. How do I make it green? Thanks:
describe('cancellation tests', () => {
function fakeFetch() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(1);
}, 100);
});
}
function awaitAndAddOne(p1) {
return p1.then(res => res + 1);
}
it('`cancel` cancels promises higher up the chain', () => {
const p1 = fakeFetch();
const p2 = awaitAndAddOne(p1);
expect(p2.isCancellable()).toBeTruthy();
p2.cancel();
return p2
.then(() => {
console.error('then');
})
.catch(err => {
console.error(err);
})
.finally(() => {
expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
expect(p1.isCancelled()).toBeTruthy();
});
});
});

Answer 1

From here:
The cancellation feature is by default turned off, you can enable it using Promise.config.
Seems like you didn't enable the cancellation flag on the Promise itself:
Promise.config({
cancellation: true
});
describe(...

Answer 2

#Karen if correct. But the issue is that your test is also a bit wrong
If you look at the isCancellable method
Promise.prototype.isCancellable = function() {
return this.isPending() && !this.isCancelled();
};
This is just checking if the promise is pending and is not already cancelled. This doesn't mean then cancellation is enabled.
http://bluebirdjs.com/docs/api/cancellation.html
If you see the above url, it quotes below
The cancellation feature is by default turned off, you can enable it using Promise.config.
And if you look at the cancel method
Promise.prototype["break"] = Promise.prototype.cancel = function() {
if (!debug.cancellation()) return this._warn("cancellation is disabled");
Now if I update your test correct like below
var Promise = require("bluebird");
var expect = require("expect");
describe('cancellation tests', () => {
function fakeFetch() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(1);
}, 100);
});
}
function awaitAndAddOne(p1) {
return p1.then(res => res + 1);
}
it('`cancel` cancels promises higher up the chain', () => {
const p1 = fakeFetch();
const p2 = awaitAndAddOne(p1);
value = p2.isCancellable();
expect(p2.isCancellable()).toBeTruthy();
p2.cancel();
expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
expect(p1.isCancelled()).toBeTruthy();
});
});
You can see that cancellation is not enable and it executes the warning code
The execution results fail as expected
spec.js:46
cancellation tests
spec.js:46
1) `cancel` cancels promises higher up the chain
spec.js:78
0 passing (3m)
base.js:354
1 failing
base.js:370
1) cancellation tests
base.js:257
`cancel` cancels promises higher up the chain:
Error: expect(received).toBeTruthy()
Expected value to be truthy, instead received
false
at Context.it (test/index.test.js:37:36)
Now if you update the code to enable cancellation
var Promise = require("bluebird");
var expect = require("expect");
Promise.config({
cancellation: true
});
describe('cancellation tests', () => {
function fakeFetch() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(1);
}, 100);
});
}
function awaitAndAddOne(p1) {
return p1.then(res => res + 1);
}
it('`cancel` cancels promises higher up the chain', () => {
const p1 = fakeFetch();
const p2 = awaitAndAddOne(p1);
value = p2.isCancellable();
expect(p2.isCancellable()).toBeTruthy();
p2.cancel();
expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
expect(p1.isCancelled()).toBeTruthy();
});
});
It works!