MultiView Control Selelct is Always null

Question

hi my dear friends :

I want to check multiview, ActiveViewIndex with Javascript,

but in the below code, MultiView is always null:

document.onkeyup = onkeyupOfDocument;

function onkeyupOfDocument(evt) {
    var evt = evt || window.event;
    var MultiView = document.getElementById("MultiView1");
    alert(MultiView);
}

How can i fix that?

thanks in future advance