var select = document.getElementById('halls');
    select.addEventListener('mouseover', function (ev) {
        select.innerHTML = '';
        var fragment = document.createDocumentFragment();
        var opt = document.createElement('option');
        opt.innerHTML = 'Choose Hall';
        opt.value = 'Choose Hall';
        fragment.appendChild(opt);
        var numberOfHalls = eventSystem.halls.length;
        for (var i = 0; i < numberOfHalls; i++) {
            opt = document.createElement('option');
            opt.innerHTML = eventSystem.halls[i].getName();
            opt.value = eventSystem.halls[i].getName();
            fragment.appendChild(opt);
        }
        select.appendChild(fragment);
        this.removeEventListener('mouseover',arguments.callee,false);
    });