Bluebird - chained promises cancel() example

bluebirdCancel.js

function a (obj) {
    return new Promise(function (res, rej) {
        res(obj);
    });
};

function chainingClosure(start){
    console.log('starting regular bluebird promise example...');

    var p = a(start)
        .then(function(val){
            console.log(val);
            return (start === 'without cancel() call') ? a('run next then') : p.cancel();
        })
        .then(function(val){
            console.log(val);
            console.log('--------------');
        })
        .cancellable()
        .catch(Promise.CancellationError, function () {
            console.log('was cancelled');
            return;
        });

    return p;
};

Promise.resolve()
    .then(function(){
        return chainingClosure('without cancel() call');
    })
    .then(function(){
        return chainingClosure('run with cancel');
    });

Hi, do you know how can I do to cancel a Promise.each() ?