php 的 ajax 实现

<script type="text/javascript" src="jquery-1.3.2.min.js"></script>
<input type="button" onclick="test();" value="提交"/>
<script type="text/javascript">
    function test(){
            var valid = {
                username: 'taoge',
                password: '123456'
            };
            $.ajax({
                url: 'valid.php',
                type: 'get',
                data: valid,   // 发送的数据
                dataType: 'json', // 发送/接收数据的格式
                success: function(data){
                    alert(""+data.username);
                },
                error: function(data){
                    alert("xxx"+data);
                }
            });
    }
</script>
===========================
valid.php