Create a drop down check box list in HTML with JavaScript

I need to create a drop down check box list like here. The problem with the code over there is that it is not working in IE9. I'm getting an error saying getElementsByClassName is not a property in the below code:

var checkList = document.getElementById('list1');
var items = document.getElementById('items');
        checkList.getElementsByClassName('anchor')[0].onclick = function (evt) {
            if (items.classList.contains('visible')){
                items.classList.remove('visible');
                items.style.display = "none";
            }

            else{
                items.classList.add('visible');
                items.style.display = "block";
            }


        }

        items.onblur = function(evt) {
            items.classList.remove('visible');
        }

Can someone please help me out on how to create a drop down check box list? Thanks.