js去除空格验证不能为空

<script language="javascript">
String.prototype.trim = function() {
 return this.replace(/(^\s*)|(\s*$)/g, "");
}
function check(){
  var v = aForm.bv.value;
  if(v.trim().length==0){
    alert("不能为空！");
  }
}
</script>

</head>
<form name="aForm">
<input type="text" name="bv" />
<input type="button" name="jj" value="check" onclick="check()" />
</form>