从jQuery中的ajax.success调用object的方法时出现问题

function modifyDatabase(tabla, id, objData, callback, arrayCallback){
    $.ajax({
        url: 'modifyDatabase.php',
        type: "POST",
        dataType: "json",
        data: 'tabla='+tabla+'&id='+id+strData,
        success: function(data){            
            callback(data);
        },
    });
}

var obj = {
    set: function (data){
        alert(this.var1);
    },
    var1: 100
}

function modifyDatabase('', '', '', obj.set, '');
function modifyDatabase(tabla, id, objData, cal