为何多行删除不了,且报错
<script>  
 function   delselchk() 
 { 
 	var   obj   =   document.getElementsByName( "chkt1 "); 
 	var   tb1=document.getElementById( "tb1 "); 
 	var   objLen=   obj.length;    
 	for   (var   i=0;   i <objLen;i++)    
 	{ 
 		if(obj[i].checked==true) 
 		{ 
 			tb1.deleteRow(document.getElementById(obj[i].value).rowIndex); 
 		} 
 	}	 
 } 
  </script>    
  <body>  
  <table   name= "tb1 "   id= "tb1 "      border=1>  
  <tr>  
  <td   id= "tr1 "   name= "tr1 ">  <input   type= "checkBox "   name= "chkt1 "   id= "chkt1 "   value= "tr1 ">  </td>  
  <td> 第一行 </td>  
  </tr>  
  <tr   id= "tr2 "   name= "tr2 ">  
  <td>  <input   type= "checkBox "   name= "chkt1 "   id= "chkt1 "   value= "tr2 ">  </td>  
  <td> 第二行 </td>  
  </tr>  
  <tr   id= "tr3 "   name= "tr3 ">  
  <td>  <input   type= "checkBox "   name= "chkt1 "   id= "chkt1 "   value= "tr3 ">  </td>  
  <td> 第三行 </td>  
  </tr>  
  </table>    
  <input   type= "button "   onclick= "delselchk() "   value= "选择后删除 ">  
  </body>
------解决方案------------------------这样就可以了-----   
  <script>  
 function delselchk() 
 { 
 	var obj = document.getElementsByName( "chkt1 "); 
 	var tb1=document.getElementById( "tb1 "); 
 	var objLen= obj.length;  
 	for (var i=objLen-1; i> -1;i--)  
 	{ 
 		if(obj[i].checked==true) 
 		{ 
 			tb1.deleteRow(document.getElementById(obj[i].value).rowIndex); 
 		} 
 	}	 
 } 
  </script>    
  <body>  
  <table name= "tb1 " id= "tb1 "  border=1>  
  <tr>  
  <td id= "tr1 " name= "tr1 ">  <input type= "checkBox " name= "chkt1 " id= "chkt1 " value= "tr1 ">  </td>  
  <td> 第一行 </td>  
  </tr>  
  <tr id= "tr2 " name= "tr2 ">  
  <td>  <input type= "checkBox " name= "chkt1 " id= "chkt1 " value= "tr2 ">  </td>  
  <td> 第二行 </td>  
  </tr>  
  <tr id= "tr3 " name= "tr3 ">  
  <td>  <input type= "checkBox " name= "chkt1 " id= "chkt1 " value= "tr3 ">  </td>  
  <td> 第三行 </td>  
  </tr>  
  </table>    
  <input type= "button " onClick= "delselchk() " value= "选择后删除 ">  
  </body>