JS Q library - defer error catching

Question

I'm discovering Kris Koval Q library and I have a problem. Look at this simple code:

function getPromise1() {
    var deferred = Q.defer();
    setTimeout(function () {
        console.log('Promise 1 OK');
        deferred.resolve();
    }, 1000);
    return deferred.promise;
}


function getPromise2() {
    var deferred = Q.defer();
    setTimeout(function () {
        console.log('Promise 2 Failed');
        deferred.reject();
    }, 1000);
    return deferred.promise;
}

getPromise1()
    .then(getPromise2())
    .fail(function () {
        alert('Fail!');
    })
    .done();

I expect to see:

Promise 1 OK
Promise 2 Failed

and then show alert "Fail!", but the alert never shows. Instead of that I see warning in my console:

[Q] Unhandled rejection reasons (should be empty): ["(no stack) undefined"] 

Why rejection is not handled and how can I handle it?

Answer 1

In the then function, you should pass just the getPromise2 function, not the result of getPromise2()

getPromise1()
    .then(getPromise2)            // NOTE: We are not calling it here
    .fail(function () {
        console.log('Fail!');
    })
    .done();