JavaScript控制CSS实现Div展开与关闭功能

<title>js操作div展开关闭</title>
<style>
  #jb51 { border: solid 1px #EEE; 
    background:#F7F7F7; 
    margin:20px; 
    padding:10px; 
    display:none;
    width:300px;    
  }
</style>
<input style="cursor:pointer" onclick="show('jb51');"
type='button' value='展开' id='inp'>
<div id="jb51">本站提供编程源码、网站源码、网页素材、
书籍教程、网站模板、网页特效代码等！</div>
<script>
function show(id){
  var aiin = document.getElementById(id);
  var inp= document.getElementById('inp');
  if(aiin.style.display != 'block'){
    aiin.style.display = 'block';
    inp.value='关闭';
  }else{
    aiin.style.display = 'none';  
    inp.value='展开';
  }
}
</script>