JS Answer check

I'm making a program that generates two random numbers and asks the user to provide the answer to the two numbers multiplied. I have managed to get the number generator to work and the correct answer is displayed but the checker isn't working correctly. I'd also like it to show a message if nothing was entered into the answer box. Any help would be great, thanks!

var x, y;

function generateNumbers() {
    function getRandom12() {
        return Math.floor((Math.random() * 12) + 1);
    }
    x = getRandom12();
    y = getRandom12();
}

function genQuestion() {
    generateNumbers();
    document.getElementById('question').value = x + " times " + y;
}

function buttonPressed() {
    if (answer == x * y)
        {
            window.alert("yes");
        }
    else {
        window.alert("no");
    }

}