simple javascript code doesn't work, can't figure out why

Question

I don't use javascript alot but this should be so simple I shouldn't fail on it but after trying to get it working for 30 minutes I need to ask for help:

I have this button

<button onclick="showMembers()">test</button> 

and this code in the < head>

    <script type="text/javascript">
function showMembers()
{
    document.getElementByID( 'MembersBox' ).style.display='block';

}
</script>

this is the html id:

<article id="MembersBox" style="display: none;" class="module width_quarter">

and I can't get it to show, nothing happens, inspecting it with firebug says nothing anywhere about javascript errors.

Answer 1

change getElementByID to getElementById

jsfiddle