Question

我获得了div标签的偏移宽度。下面是代码。

 <body>
  <div id="marqueeborder" onmouseover="pxptick=0" onmouseout="pxptick=scrollspeed">
<div id="marqueecontent">


<?php

    // Original script by Walter Heitman Jr, first published on http://techblog.shanock.com

    // List your stocks here, separated by commas, no spaces, in the order you want them displayed:
    $stocks = "idt,iye,mill,pwer,spy,f,msft,x,sbux,sne,ge,dow,t";

    // Function to copy a stock quote CSV from Yahoo to the local cache. CSV contains symbol, price, and change
    function upsfile($stock) { copy("http://finance.yahoo.com/d/quotes.csv?s=$stock&f=sl1c1&e=.csv","stockcache/".$stock.".csv"); }

    foreach ( explode(",", $stocks) as $stock ) {

        // Where the stock quote info file should be...
        $local_file = "stockcache/".$stock.".csv";

        // ...if it exists. If not, download it.
        if (!file_exists($local_file)) { upsfile($stock); }
        // Else,If it's out-of-date by 15 mins (900 seconds) or more, update it.
        elseif (filemtime($local_file) <= (time() - 900)) { upsfile($stock); }

        // Open the file, load our values into an array...
        $local_file = fopen ("stockcache/".$stock.".csv","r");
        $stock_info = fgetcsv ($local_file, 1000, ",");

        // ...format, and output them. I made the symbols into links to Yahoo's stock pages.
        echo "<span class=\"stockbox\"><a href=\"http://finance.yahoo.com/q?s=".$stock_info[0]."\">".$stock_info[0]."</a> ".sprintf("%.2f",$stock_info[1])." <span style=\"";
        // Green prices for up, red for down
        if ($stock_info[2]>=0) { echo "color: #009900;\">&uarr;";   }
        elseif ($stock_info[2]<0) { echo "color: #ff0000;\">&darr;"; }
        echo sprintf("%.2f",abs($stock_info[2]))."</span></span>\n";
        // Done!
        fclose($local_file); 
    }
?>
<span class="stockbox" style="font-size:0.6em">Quotes from <a href="http://finance.yahoo.com/">Yahoo Finance</a></span>

</div>
</div>
 </body>

下面是javascript函数，它将在页面上调用。

<script type="text/javascript">

    // Original script by Walter Heitman Jr, first published on http://techblog.shanock.com

    // Set an initial scroll speed. This equates to the number of pixels shifted per tick
    var scrollspeed=2;
    var pxptick=scrollspeed;

    function startmarquee(){
        alert("hi");
        // Make a shortcut referencing our div with the content we want to scroll
        var marqueediv=document.getElementById("marqueecontent");
        alert("marqueediv"+marqueediv);
        alert("hi"+marqueediv.innerHTML);

        // Get the total width of our available scroll area
        var marqueewidth=document.getElementById("marqueeborder").offsetWidth;
        alert("marqueewidth"+marqueewidth);
        // Get the width of the content we want to scroll
        var contentwidth=marqueediv.offsetWidth;
        alert("contentwidth"+contentwidth);
        // Start the ticker at 50 milliseconds per tick, adjust this to suit your preferences
        // Be warned, setting this lower has heavy impact on client-side CPU usage. Be gentle.
        var lefttime=setInterval("scrollmarquee()",50);
        alert("lefttime"+lefttime);
    }

    function scrollmarquee(){
        // Check position of the div, then shift it left by the set amount of pixels.
        if (parseInt(marqueediv.style.left)>(contentwidth*(-1)))
            marqueediv.style.left=parseInt(marqueediv.style.left)-pxptick+"px";
        // If it's at the end, move it back to the right.
        else
            marqueediv.style.left=parseInt(marqueewidth)+"px";
    }

    window.onload=startmarquee();

</script>

当iam在服务器上运行上面的代码时，我在第46行得到javascript错误“需要对象”警报（“marqueediv”+ marqueediv）;在发出javascript错误的警报之后是“marqueedivnull”。

我的问题是，div标签是否未被识别？为什么？所以只有它作为空对象，我怎么能解决这个问题？

感谢。

Answer 1

您立即致电startmarquee并尝试将其返回值（undefined）分配给window.onload。

据推测，脚本出现在<head>中，并且在运行时div不存在。

将函数分配给onload，而不是其返回值。

window.onload=startmarquee;

Answer 2

您可以复制脚本并将其放在正文结束标记之前并删除window.onload=startmarquee();，从而确保所有元素都已加载并可访问

就像@Quentin所说的那样，当你引用它时，带有id的元素可能没有被加载到DOM中

获取所需的javascript错误对象

2 个答案: