AJAX没有加载 - 在机智的结束

Question

好的，对于一直在跟踪此问题的人：感谢您的耐心和帮助。我完全重做这个问题，希望能够提供答案，见解，甚至只是一个理论。为了呈现我的XML代码，我将其简化为仅重现问题所需的元素。

正如我在原始帖子中所解释的那样，XML文件用于在学期＆gt;课程＆gt;单元＆gt;文本层次结构中存储学术课程的数据。这是一个最小的例子：

 <MLIS>
    <semester>
        <semesterInfo>
            <semNumber>1</semNumber>
            <season>Spring</season>
            <semYear>2014</semYear>
        </semesterInfo>
        <courses>
            <course>
                <courseInfo>
                    <department>IRLS</department>
                    <courseNumber>504</courseNumber>
                    <courseTitleInfo>
                        <courseTitle>Foundations</courseTitle>
                    </courseTitleInfo>
                </courseInfo>
                <units>
                    <unit>
                        <unitInfo>
                            <unitNumber>1</unitNumber>
                            <unitTitle>Introductions</unitTitle>
                        </unitInfo>
                        <unitMaterial>
                            <resource>
                                <type>video lecture</type>
                                <titleInfo>
                                    <title>Pre-course lecture</title>
                                </titleInfo>
                                <authorInfo>
                                    <author>
                                         <firstName>Joe</firstName>
                                         <lastName>Blow</lastName>
                                         <displayForm>Blow</displayForm>
                                    </author>
                                </authorInfo>
                                <dateInfo>
                                    <dateIssued>Aug 13, 2013</dateIssued>
                                </dateInfo>
                                <extent>
                                    <time>
                                       <minutes>14</minutes>
                                       <seconds>17</seconds>
                                    </time>
                                </extent>
                                <competency>
                                    <comp>n/a</comp>
                                </competency>
                                <link></link>
                           </resource>
                        </unitMaterial> 
                    </unit>
                </units>
            </course>
            <course>
                <courseInfo>
                    <department>IRLS</department>
                    <courseNumber>515</courseNumber>
                    <courseTitleInfo>
                        <courseTitle>Org ofInfo</courseTitle>
                    </courseTitleInfo>
                </courseInfo>
                <units>
                    <unit>
                        <unitInfo>
                            <unitNumber>1</unitNumber>
                            <unitTitle>Course Overview</unitTitle>
                        </unitInfo>
                        <unitMaterial>
                            <resource>
                                <type>book chapter</type>
                                <titleInfo>
                                    <title>Org of Recorded Inf</title>
                                </titleInfo>
                                <authorInfo>
                                    <author>
                                        <firstName>Arlene G.</firstName>
                                        <lastName>Taylor</lastName>
                                    </author>
                                    <author>
                                        <firstName>Daniel</firstName>
                                        <lastName>Joudrey</lastName>
                                    </author>
                                </authorInfo>
                                <dateInfo>
                                    <dateIssued>2008</dateIssued>
                                </dateInfo>
                                <extent>
                                    <pages>
                                        <numberPgs>33</numberPgs>
                                    </pages>
                                </extent>
                                <hostWork>
                                    <book>
                                        <titleInfo>
                                            <title>The Org ofInfo</title>
                                            <subTitle>3rd Ed</subTitle>
                                        </titleInfo>
                                        <author>
                                            <firstName>Arlene</firstName>
                                            <lastName>Taylor</lastName>
                                        </author>
                                        <originInfo>
                                            <publisher>LibUnl</publisher>
                                            <place>Westport, Conn</place>
                                        </originInfo>
                                    </book>
                                </hostWork>
                                    <competency>
                                        <comp>n/a</comp>
                                    </competency>
                            </resource>
                        </unitMaterial>
                    </unit>
                </units>
            </course>
        </courses>
    </semester>

    <semester>
        <semesterInfo>
            <semNumber>2</semNumber>
            <season>Summer</season>
            <semYear>2014</semYear>
        </semesterInfo>
        <courses>
            <course>
                <courseInfo>
                    <department>IRLS</department>
                    <courseNumber>540</courseNumber>
                    <courseTitleInfo>
                        <courseTitle>Intro to Archives</courseTitle>
                    </courseTitleInfo>
                </courseInfo>
                <units>
                <unit>
                    <unitInfo>
                        <unitNumber>1</unitNumber>
                        <unitTitle>History and Theory</unitTitle>
                    </unitInfo>
                    <unitMaterial>
                        <resource>
                            <type>book chapter</type>
                            <titleInfo>
                                <title>Metadata: Description</title>
                            </titleInfo>
                            <authorInfo>
                                <author>
                                    <firstName>Arlene G.</firstName>
                                    <lastName>Taylor</lastName>
                                </author>
                                <author>
                                    <firstName>Daniel N.</firstName>
                                    <lastName>Joudrey</lastName>
                                </author>
                            </authorInfo>
                            <dateInfo>
                                <dateIssued>2008</dateIssued>
                            </dateInfo>
                            <extent>
                                <pages>
                                    <numberPgs>45</numberPgs>
                                </pages>
                            </extent>
                            <hostWork>
                                <book>
                                    <titleInfo> 
                                        <title>The Org of Inf</title>
                                        <subTitle>Third Ed</subTitle>
                                    </titleInfo>
                                    <author>
                                        <firstName>Arlene</firstName>
                                        <lastName>Taylor</lastName>
                                    </author>
                                    <originInfo>
                                        <publisher>Lib Unl</publisher>
                                        <place>Westport, Conn</place>
                                    </originInfo>
                                </book>
                            </hostWork>   
                            <competency>
                                <comp>n/a</comp>
                            </competency>
                        </resource>
                    </unitMaterial>
                </unit>
            </units>
        </course>
    </courses>
    </semester>
</MLIS>

我在星期五之前得到的是一个HTML页面，它显示每个学期，每个课程，每个课程中的所有单元，以及每个单元内的所有文本（资源）。我使用jQuery toggle（）在每个级别显示和隐藏。

现在页面只显示第一个学期。循环不再拿到第二学期，我不知道为什么。我真的很想解决这个问题。