test.js

var Promise = require('bluebird');
var superagent = Promise.promisifyAll(require('superagent'));

function a(obj) {
    return superagent
        .get('http://google.com')
        .endAsync();
};

function chainingClosure(start) {
    var p = a(start)
        .then(function (val) {
            console.log('run first then.. ' + val.status);
            return (start === 'without cancel() call') ? a('running next then') : p.cancel();
        })
        .then(function (val) {
            console.log(val.status);
            console.log('--------------');
        })
        .cancellable()
        .catch(function () {
            console.log('was cancelled');
        });

    return p;
};

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