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我有一個頁面，主要是由Ajax生成的動態內容。它每30秒隨機化一次，並從數據庫中出現新內容。 PHP似乎很好，但或者似乎有我的Javascript代碼有問題，或者數據庫有問題導致它滯後（Ajax需要大約30秒才能加載！）
看起來好像遞歸調用到setInterval在我的Javascript中等待分配毫秒之前執行該功能，但我無法在我的Javascript中找到任何錯誤。
此外，從數據庫中檢索到兩個圖像url字符串，並且似乎有理由認爲Ajax在必須從外部來源檢索信息時會滯後。
或者，也許我的PHP-MySQL語法的使用存在滯後性ORDER BY rand()？
下面是相關的html：
這個Ajax爲什麼需要這麼長時間才能呈現？
<html>
<head>
<title></title>
<script type = "text/javascript" src = "randomProducts.js" />
<script type = "text/javascript">
setIntervalOnload();
</script>
</head>
<body>
...
...
...
</body>
</html>
下面是相關的Javascript：
// global static variables
var subCategory; // initialized from setCategoryTree
var t; // for setInterval and clearInterval
var seconds;
var millisecondsPerSecond;
var milliseconds;
function setIntervalOnload()
{
getRandomProducts();
if(typeof t != "undefined")
clearInterval(t);
seconds = 30;
millisecondsPerSecond = 1000;
milliseconds = seconds * millisecondsPerSecond;
t = setInterval(getRandomProducts, milliseconds);
}
function getRandomProducts()
{
//window.alert(subCategory);
if(typeof subCategory == "undefined")
subCategory = "all";
else
{
clearInterval(t);
t = setInterval(getRandomProducts, milliseconds);
}
var req = new XMLHttpRequest();
var products = document.getElementById("products");
req.onreadystatechange = function()
{
if((req.readyState == 4) && (req.status == 200))
{
var result = req.responseText;
products.innerHTML = result;
}
};
req.open("GET", "randomProducts.php?category=" + subCategory, true);
req.send(null);
}
function setCategoryTree(link)
{
var categoryTree = document.getElementById("categoryTree");
/* climbing the DOM-tree to get the category name (innerHTML of highest "a" tag) */
var category = link.parentNode.parentNode.parentNode.getElementsByTagName("a")[0].innerHTML;
subCategory = link.innerHTML;
categoryTree.innerHTML = "==> " + category + " ==> " + subCategory;
getRandomProducts();
}
...這裏是相關PHP：
<?php
// connect to MySQL
$dbName = "blah";
$db = mysql_connect("localhost", $dbName, "asdf");
if (!$db)
{
echo "<p>Error - Could not connect to MySQL</p>";
exit;
}
// select the blah database
$blah = mysql_select_db("blah");
if(!$blah)
{
echo "<p>Error - Could not select the blah database.</p>";
exit;
}
// fix html characters in $subCategory
$subCategory = $_GET["category"];
trim($subCategory);
$subCategory = stripslashes($subCategory);
$subCategoryFixed = htmlspecialchars($subCategory);
// for loop for each random product (total of 10 random products)
for($i = 0; $i < 10; $i++)
{
// query the blah database for all products
if($subCategoryFixed == "all")
{
$query = "SELECT * FROM products ORDER BY rand();";
$result = mysql_query($query);
}
else // query the blah database for products in selected subCategory
{
$query = "SELECT * FROM products WHERE cat = " . $subCategoryFixed . " ORDER BY rand();";
$result = mysql_query($query);
}
if (!$result)
{
echo "<p>Error - the query could not be executed</p><br />";
$error = mysql_error();
echo "<p>" . $error . "</p>";
exit;
}
$row = mysql_fetch_array($result);
$productValues = array_values($row);
$name = htmlspecialchars($productValues[3]);
$price = htmlspecialchars($productValues[5]);
$img = htmlspecialchars($productValues[7]);
// product info is formatted for home.html here
$str = '<div>
<a href = "' . $link . '" title = "' . $name . '">
<table id = "product-table" onmouseover = "darkenProduct(this);" onmouseout = "lightenProduct(this);">
<tr>
<td>' . $name .'</td>
</tr>
<tr>
<td><img src = "' . $img . '" /></td>
</tr>
<tr>
<td>' . $price . '</td>
</tr>
</table>
</a>
</div>';
echo $str;
} // end of products for loop
?>
'爲了（）'是出了名的慢，做的任意列一個簡單的測試和秩序，看看您的問題不見了。 – 2012-04-18 02:02:14
你沒有在onload方法中運行你的代碼。 AJAX設置代碼運行速度可能比頁面加載速度快，所以'var products = ...'爲空。嘗試使用控制檯在Chrome中運行（CTRL + SHIFT + J）並查看是否記錄了任何錯誤消息。 – mellamokb 2012-04-18 02:08:43
好的，謝謝，已經在控制檯中運行Chrome，並顯示如下錯誤消息：'無法加載資源：服務器響應狀態爲404（未找到）'，'Uncaught ReferenceError：$未定義'未捕獲的TypeError：無法設置null的屬性'innerHTML'...所以它看起來好像'var products'爲null。但是，我已經嘗試執行Ajax函數本身**第一**，而不是從另一個函數調用它，並沒有區別... – 2012-04-18 02:31:55