(currentStyle)javascript Why sometimes I can't get the set CSS attributes when using style_javascript skills

This is when the blue horizontal bar is clicked for the second time before the effect starts, which means that the first click does not get foot.style.display=="none", but in CSS I defined
#top {width:100px; background-color:#00CCFF; height:20px}
#foot {width:100px; background-color: #CCCC00; height:50px; display:none}

<script> <BR><!-- <BR>function qa(){ <BR>if (foot.style.display=="none") { <BR>foot.style.display="block";}; <BR>else { <BR>foot.style.display="none";} <BR>} <BR>--> <BR></script>