JAVASCRIPT 数字,负数,小数

<input name="input" type="text" onkeyup="JHshNumberText(this)" id="title">
<br>

<script language="javascript" type="text/javascript">
function JHshNumberText(a)
{
  var fa="";
  if(a.value.substring(0,1)=="-")
      fa="-";

  var str=(a.value.replace(/[^0-9.]/g,'')).replace(/[.][0-9]*[.]/, '.');
 

  if (str.substring(0,1)==".")
   str="0"+str;
   a.value=fa+str;

}
</script>