JavaScript实现文本框中默认显示背景图片在获得焦点后消失的方法

<p class="contain">
 <p class="inputFullNameContain"><input class="inputFullName" type="text" id="search_content" /> </p>
 </p>

 <script type="text/javascript" >
 (function () {
 var id = document.getElementById('search_content');
 if (id) {
 var name = id;
 var unclicked = function () {
 if (name.value == '') {
 name.style.background = 'url("images/inputBackground.png") no-repeat center';
 }
 };
 var clicked = function () {
 name.style.background = 'none';
 };
 name.onfocus = clicked;
 name.onblur = unclicked;
 unclicked();
 }
 })();
</script>