Javascript未定义错误（在HTML页面中加载JSONP）

我有一个关于将JSONP加载到HTML的问题

这是我的JSONP文件：

myCallback({
"news": {
    "item": [
        {
            "Title": "IceBridge Preparations Continue",
            "Author": "George Hale, IceBridge Science Outreach Coordinator",
            "Date": "14/09/2012",
            "Intro": "The work of installing IceBridge's science instruments on the NASA DC-8 airborne laboratory continued this week.",
            "Content": "People from the Center for the Remote Sensing of Ice Sheets at the University of Kansas (CReSIS) and from Sander Geophysics Limited (SGL) spent the week installing the aircraft's various radar instruments and the AirGrav gravimeter. With the last of the instruments installed and operational, IceBridge is now ready to start test flights next week. Monday afternoon's schedule includes pilot proficiency flights and on Tuesday and Wednesday IceBridge will carry out instrument check flights."
        },
        {
            "Title": "Preparing the DC-8 for Antarctica 2012",
            "Author": "George Hale, IceBridge Science Outreach Coordinator",
            "Date": "20/09/2012",
            "Intro": "Over the next few weeks the IceBridge team will prepare NASA's DC-8 airborne laboratory for the 2012 Antarctic campaign.",
            "Content": "Long hours in the hangar at NASA's Dryden Flight Research Facility mean that the MCoRDS antenna and Airborne Topographic Mapper have been installed and all ground tests for ATM are complete. Next week, the radar and gravimeter teams will begin their preparation work."
        },
        {
            "Title": "Q&A: Michael Studinger",
            "Author": "Maria-Jose Viñas, Cryospheric Sciences Laboratory Outreach Coordinator",
            "Date": "30/09/2012",
            "Intro": "Michael Studinger is Operation IceBridge’s project scientist.",
            "Content": "He trained as a geophysicist in Germany, his home country, before moving to the U.S. to take a position at the Lamont-Doherty Earth Observatory and then transferring to NASA Goddard Space Flight Center in 2010. Studinger has been studying polar regions for 18 years, expanding his initial focus on the geology and tectonics of the Antarctic continent to the overall dynamic of polar ice sheets."
        }
    ]
}

})

现在我想把它加载到HTML页面中

我使用Javascript实现这一点：

<script type="text/javascript">

function myCallback(data)
{
    var htmlContent;
    $.each(data.news.item,function(index, item)
    {
    htmlContent += "<article>" + "<h1>" + item.Title + "</h1>";
    htmlContent += "<h2>" + item.Author + "</h2>";
    htmlContent += "<p><i>" + item.Date + "</i></p>";
    htmlContent += "<p>" + item.Intro + "</p>";
    htmlContent += "<p>" + item.Content + "</p>" + "</article>";
    });
    $("#main").html(htmlContent);
}

函数myCallback（数据）
{
var-htmlContent；
$.each（data.news.item，函数（索引，项）
{
htmlContent+=“”+“”+项。标题+“”；
htmlContent+=“”+项。作者+“”；
htmlContent+=“”+项目日期+”
”；
htmlContent+=“”+item.Intro+”
”；
htmlContent+=“”+项.内容+”
“+”；
});
$（“#main”）.html（htmlContent）；
}

在正文中我有

这一切都是正确的，但我总是在html页面的顶部未定义，然后在json文件中未定义文本。有人知道我如何解决这个问题吗？

这个：

var htmlContent;

应该是这样的：

var htmlContent = '';

没有值的声明变量是

未定义的

。发生的事情是，当你这样做：

htmlContent += "<article>";

htmlContent+=”；

您基本上是在做

htmlContent=undefined+“”

。JS将

未定义的
强制添加到一个字符串中，以将其添加到另一个字符串中

将变量初始化为空字符串可防止这种情况发生。
我不确定这是否能解决问题，但您可能需要先初始化您的htmlContent字符串
htmlContent=“”，然后再添加。
@user1775531如果某个答案有助于解决堆栈溢出问题，您应该通过单击该答案旁边的复选标记来接受该答案。