onfocus="if(this.value=='请输入图片说明'){this.value=''}"失效了，为什么

[fkueyga6]

<input type="button" value="增加内容" onClick="addNew_nr();">
......省略
<textarea name="p_nr_1" rows="5" id="p_nr_1" style="width:100%; height:100px; color: #666;" onfocus="if(this.value=='请输入图片说明'){this.value=''}" onblur="if(this.value==''){this.value='请输入图片说明'}">请输入图片说明</textarea>
.........省略 //onfocus和onblur在这里有效

<script type="text/javascript">
function addNew_nr()
{
var table1 = $('#xianmu_nr');
var firstTr = table1.find('tbody>tr:first');
var row = $("<tr id='tr_"+nr_count+"'></tr>");
var td = $('<td width="120" height="120" align="center" valign="middle"><textarea name="nr_'+nr_count+'" rows="5" id="nr_'+nr_count+'" style="width:100%; height:100px; color: #666;" onfocus="if(this.value=="请输入图片说明"){this.value=""}" onblur="if(this.value==""){this.value="请输入图片说明"}">请输入图片说明</textarea></td>');
...............省略 //onfocus和onblur在这里新增加出来以后就失效了，请问为什么
}
</script>

[天际的海浪]

var td = $('<td width="120" height="120" align="center" valign="middle"><textarea name="nr_'+nr_count+'" rows="5" id="nr_'+nr_count+'" style="width:100%; height:100px; color: #666;" onfocus="if(this.value==\'请输入图片说明\'){this.value=\'\'}" onblur="if(this.value==\'\'){this.value=\'请输入图片说明\'}">请输入图片说明</textarea></td>');

[天际的海浪]

或者是 var td = $('<td width="120" height="120" align="center" valign="middle"><textarea name="nr_'+nr_count+'" rows="5" id="nr_'+nr_count+'" style="width:100%; height:100px; color: #666;" onfocus=\'if(this.value=="请输入图片说明"){this.value=""}\' onblur=\'if(this.value==""){this.value="请输入图片说明"}\'>请输入图片说明</textarea></td>');