为什么我的jquery对话框使用延迟而不等待用户选择?

我有以下函数,它创建一个对话框,并使用jquery deferred等待用户响应:

function myPageUnsaved() {
    var defer = $.Deferred();
    $('<div></div>')
    .html('You have unsaved changes. Leave this page and lose your changes?')
    .dialog({
        autoOpen: true,
        modal: true,
        title: 'Confirmation',
        buttons: {
            "No": function () {
                defer.resolve("false");
                $(this).dialog("close");
             },
             "Yes": function () {
                defer.resolve("true");
                $(this).dialog("close");
             }
        },
        close: function () {
            $(this).dialog('destroy').remove();
        }
    });
    return defer.promise();
}

我调用下面JS中的函数:

// function to check for user changes prior to navigating to a new page
function checkPageChange() {
    if (pageChanges == true) {
        myPageUnsaved().then(function (answer) {
            // if user answered no, stay on the page
            if(answer == 'false') {
                return false;
            // else the user answered yes, so leave the page
            } else {
                return true;
            }
        });

    } else {
        return true;
    }
}   

我正在运行jquery 1.11。

对话框将显示给用户,但会立即删除。我错过了什么?