JavaScript : 동일네임의 id를 알아내기(class 사용해서 해결)

<div class="menu_a"></div>
<div class="menu_a"></div>
<div class="menu_a"></div>
<script language="JavaScript">
<!--
function getElementsByClassName1(className) {
    var children = document.getElementsByTagName('*') || document.all;
    var elements = [];
    for(var i=0, l=children.length; i<l; i++) {
        var childClass = (children[i].className) ? children[i].className.split(' ') : false;
        if(childClass)
            for(var n=0, m=childClass.length; n<m; n++)
                if(childClass[n] == className) elements.push(children[i]);
    }
    return elements;

}

elements = getElementsByClassName1("menu_a");
alert(elements.length)
//-->
</script>