how to use q.js promises to work with multiple asynchronous operations

function addAsync(a, b) {
    var deferred = Q.defer();
    // Wait 2 seconds and then add a + b
    setTimeout(function() {
        deferred.resolve(a + b);
    }, 2000);
    return deferred.promise;
}

Q.all([
    addAsync(1, 1),
    addAsync(2, 2),
    addAsync(3, 3)
]).spread(function(result1, result2, result3) {
    console.log(result1, result2, result3);
});
// logs "2 4 6" after approximately 2 seconds