js自动查找select下拉的菜单并选择

function find_select(name)
{
	var select = document.getElementsByName(name);
	var find_str = document.getElementById('to_find_str').value;
	if(select)
	{
		select = select[0];
		var child = select.childNodes;
		var can=false,text='',len=child.length,is_end=true;
		for(var i=0;i<len;i++)
		{
			if(can)
			{
				text = child[i].text;
				if(	text &&
					text.indexOf(find_str)!=-1)
				{
					//console.log(text);
					child[i].selected = true;
					var v = child[i].value;
					select.value = v;
					select.onchange(v);
					is_end = false;
					break;
				}
			}
			if(child[i].selected)
				can = true;
		}
		if(is_end)
			alert('已没有匹配内容');
	}
}

<tr>
          <td><?php echo $L_SpecialActivityIdentifier?></td>
          <td>
		  <select name="Activity[Identifier]" id="Identifier" onchange="change_activity(this.value)">
			<option value="">请选择</option>
			<?php
			foreach ($ActivityTypes as $Row ) {
				echo '<option value="'.$Row['Identifier'].'" '.($Row['Identifier']==$Activity['Identifier']?'selected':'').'>'.$Row['Name'].'</option>';
			} 
			?>
		  </select>
		   -- <input value='' id='to_find_str' size=16 style="text-align:center;" /><input value='find' onclick='find_select("Activity[Identifier]")' type=button />
          </td>
      </tr>