自动格式化日期js

<script  type="text/javascript" language="javascript">
    isDataTime = function (e,obj) {
    try{    
        var key;
        if ((document.all) ? true:false)
        {
            key = event.keyCode;
        }
        else
        {
            key = e.which;
        }

        if ( (key > 47) && (key < 58) )
        {
            var otext = obj.value;                    //已有的值
            var keytext = String.fromCharCode(key);   //当前输入的值
            
            //begin
            
               if(otext.length == 3)    //年
               {
                    var val = otext + keytext;
                    var t = parseInt(val);
                        if(t >= 2050)
                         obj.value = " " + otext + "年" + keytext;
                        else
                         obj.value = otext + keytext + "年";
                     return false;
               }
               else if(otext.length == 5) //月的第一位
               {
                    var val = keytext;
                    var t = parseInt(val);
                    if(t > 1)
                    {
                        obj.value = otext.substring(0,5) + "0" + keytext + "月";
                        return false;
                    }
               }
               else if(otext.length == 6) //月的第二位
               {
                    var val = otext.substring(5,6) + keytext;
                    var t = parseInt(val);
                    if(t > 12)
                        obj.value = otext.substring(0,5) + "0" + otext.substring(5,6) + "月" + keytext;
                    else
                        obj.value = otext + keytext + "月";
                    return false;
               }
               else if(otext.length == 8) //日的第一位
               {
                    var val = keytext;
                    var t = parseInt(val);
                    if(t > 3)
                    {
                        obj.value = otext.substring(0,8) + "0" + keytext + "日 ";
                        return false;
                    }
               }
               else if(otext.length == 9)//日的第二位
               {
                    var val = otext.substring(8,9) + keytext;
                    var t = parseInt(val);
                    if(t > 31)
                        obj.value = otext.substring(0,8) + "0"  + otext.substring(8,9) + "日 " + keytext;
                    else
                        obj.value = otext + keytext + "日 ";
                    return false;
               }
               else if(otext.length == 12) //时的第一位
               {
                    var val = keytext;
                    var t = parseInt(val);
                    if(t > 2)
                    {
                        obj.value = otext.substring(0,12) + "0" + keytext + "时";
                        return false;
                    }
               }
               else if(otext.length == 13)//时的第二位
               {
                    var val = otext.substring(12,13) + keytext;
                    var t = parseInt(val);
                    if(t >= 24)
                        obj.value = otext.substring(0,12) + "0" + otext.substring(12,13) + "时" + keytext;
                    else
                        obj.value = otext + keytext + "时";
                    return false;
               }
               else if(otext.length == 15) //分的第一位
               {
                    var val = keytext;
                    var t = parseInt(val);
                    if(t > 5)
                    {
                        obj.value = otext.substring(0,15) + "0" + keytext + "分";
                        return false;
                    }
               }
               else if(otext.length == 16)//分
               {
                    var val = otext.substring(15,16) + keytext;
                    var t = parseInt(val);
                    if(t > 59)
                        obj.value = otext.substring(0,15) + "0" + keytext + "分";
                    else
                        obj.value = otext + keytext + "分";
                    return false;
               }   
               else if (otext.length > 17)
                    return false;
               else
               {
                    return true;
               }                    
            //end
         }
         else if(key == 8)
         { 
            return true;
         }
         else
         {
            return false;
         }
       }
       catch(e)
       {
            alert(e);
       }
     }
</script>
<input style="width:160px;" onkeypress="javascript:return isDataTime(event,this);" />

 测试环境：IE 8， Firefox 3.5.2