bluebird promise catch() is not calling inner function with Promise.CancellationError

Question

When a file is missing, I am trying to cancel the promise. However, when I do this I see in the output:

Unhandled rejection Error: ENOENT, open '/home/one/github/infrastructure_manager_ui/gulp/util/token-file.json'
  at Error (native)

and also createTokenFile() does not run as it should. Not sure what I am doing wrong:

 function refreshToken() {
        var tokenFile = path.join(__dirname, 'token-file.json');
        return tokenPromise = fs.readFileAsync(tokenFile, {encoding: 'utf-8'})
        .then(JSON.parse)
        .cancellable()
        .catch(Promise.CancellationError, function(err) {
            console.log(err);
            if (err.code !== 'ENOENT') { 
                throw err;
            } else {
                createTokenFile();
                tokenPromise.cancel();
            }
        });
}

Why are you trying to cancel a promise from it's own handler?! — Bergi, Mar 10 '15 at 05:07

score 1 · Answer 1 · answered Mar 10 '15 at 04:29

1

.cancellable() is not doing anything here. .cancellable() turns a promise into one can be manually cancelled. You're not doing anything to cancel it here, so it's not being cancelled.

If you want to catch the file read error, you should just catch it:

function refreshToken() {
        var tokenFile = path.join(__dirname, 'token-file.json');
        return tokenPromise = fs.readFileAsync(tokenFile, {encoding: 'utf-8'})
        .then(JSON.parse)
        .catch(function(err) {
            console.log(err);
            if (err.code !== 'ENOENT') { 
                throw err;
            } else {
                return createTokenFile();
            }
        });
}

answered Mar 10 '15 at 04:29

JLRishe

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No, I need to cancel the promise also. I tried `tokenPromise.cancel();` from inside the else block but no luck – dman Mar 10 '15 at 04:33
2

@dman You can't cancel a promise that has already completed, which it would be if you were already inside that else block. And execution will not even enter that `catch` handler in your code unless the promise was already cancelled. You seem to be misunderstanding what promise cancellation does. Please see [this answer](http://stackoverflow.com/questions/28487148/promise-cancellation-still-firing-fulfill-function/28487478#28487478) for a clarification. – JLRishe Mar 10 '15 at 04:51

bluebird promise catch() is not calling inner function with Promise.CancellationError

1 Answers1