<script>
    function search() {
        
        var a=$("#search").val();
        url = "/plus/search.php?q=" + a ;
        location.href = url;
    }
</script>
                 <input type="text" id="search" class="inputbox" value="请输入您要搜索的信息"/>
                
                <input type="button" class="btn_search" value="搜索" onclick="search()" />

<script type="text/javascript">
    onload = function ()
    {
        var txt = document.querySelector ("input[type=text]");
        txt.onfocus = function ()
        {
            this.place = this.value;
            this.value = "";
        };
         
        txt.onblur = function ()
        {
            this.value = this.place;
        }
    }
</script>