How to assign a value to a global variable in ajax,and not with "async:flase"

Question

Below comes the codes.

function callPublish(authorId){
    var _shareDetail = artEditor.getContent();
    document.getElementById("shareAuthorIdInput").value = authorId;
    document.getElementById("shareDetailInput").value = _shareDetail;
    var detailData = {
        data:JSON.stringify({
            "shareTitle":$("#shareTitleInput").val(),
            "shareAuthorId":$("#shareAuthorIdInput").val(),
            "shareDetail":$("#shareDetailInput").val()
        })
    };

    $.ajax({
            url:"/pubShare",
            type: 'POST',
            data: detailData,
            success: function (msg) {
                alert(msg);
                status = msg;
            }
    });
    return status;
}

The variable "status" was defined before function callPublish(). I want to assign the returned value to the global variable "status".I try to add this into ajax: "async:false",and surprisingly,it works. But it is not asynchronous.So how can I make it work,not using "async:false"?

Thanks, my English is not so well,hoping you can get what I mean.