警告ajax响应

I am trying to read the response of ajax request in codeigniter, but couldn't do so uptill now, I have tried to many ways, but failed (stringify, console.log)

controller to which ajax request is sent

function func()
{
    echo json_encode("a");
}

ajax request

$.ajax({
    type: "POST",
    url: "<?php echo base_url(); ?>/index.php/file/func",
    data: {},
    success: function(result){
        //how to alert "a" here??????
    },
});

help please

It is json_encode instead of json_encoded and

change: //how to alert "a" here????? to: alert(result);