input输入限制

1:只能输入两位小数点：
function keepTwoPointNum(that){
   var val=that.value;
   if(isNaN(val)){
      $(that).val('');
      return
   }
   if(val.split('.')[1]){
        val=val.split('.')[0]+'.'+val.split('.')[1].substring(0,2);
        $(that).val(val);
   }
}