文本框获取焦点事件！

function _click(i){
var o=document.getElementsByTagName("input");
o(i).focus();
}_click(0);
<html>
<head>
    <title> </title>
<script>
function i2Focus(){
document.getElementById("i2").focus();
}
</script>
</head>
<body>
  <input type="text" id="i1">
  <input type="text" id="i2">
  <input type="button" id="b1" onClick="i2Focus()" value="点击">
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Untitled Page</title>
</head>
<body><table id="tab1">
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
</table>
<table id="tab2">
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
<tr> <td> <input type="text" > </td> </tr>
</table>
<input type="button" onclick="getFocus()"> <script type="text/javascript">
function getFocus(){
    document.getElementById('tab2').getElementsByTagName('input')[0].focus();
}
</script>
</body>
</html>