我的概念挣扎当我第一次开始时如何构造这样的代码。虽然它不是特定于您的特定变量,但下面是如何使用jQuery/PHP通过AJAX更新var的简单示例。
序幕:如果这是你将要经常做的事情,你要学习jQuery的,而不是单独使用普通的JavaScript。关于如何学习jQuery,有很多很棒的免费资源。另外,如果你对在线免费教程不满意,this是一本很好的书。我将在jQuery中编写示例。
设计:好了,所以它的工作方式是这样的:
在JavaScript中设置一个计时器,以执行特定的功能每X秒(你不想做的每一秒钟)。
该函数对服务器上的.PHP文件进行AJAX调用(使用jQuery),向其发送必要的数据,以便.PHP代码知道要发回的内容。
.PHP代码抓取所需的数据(例如,使用MySQL)以JSON格式对其进行编码,然后退出。
对AJAX调用的承诺被触发,并从PHP发送的数据被接收。如你所愿处理它。
从第2步
如果你有什么代码做任何的问题重复,请询问。
AJAX。PHP
<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
$return_obj = array();
$request_obj = NULL;
// our AJAX call used "POST" as it's 'type', so we look in that
// variable.
if (array_key_exists("func",$_POST)) {
if ($_POST['func'] === "get_update") {
if (array_key_exists("which_var",$_POST)) {
$which_var = $_POST['which_var'];
$which_var = $mysqli->real_escape_string($which_var); // should use prepared statements
// we sent 'num_people_logged_in' as our value here, so we'll be looking for a column/field
// with that value. this assumes that some other code, somewhere else,
// is regularly updating the table. it also assumes that there will only
// be a single row returned, which will hold the value.
$query = "SELECT '$which_var' FROM site_stats ";
if ($result = $mysqli->query($query)) {
if ($row = $result->fetch_assoc()) {
$request_obj[$which_var] = $row[$which_var];
}
}
}
}
}
$return_obj['request'] = $request_obj;
echo json_encode($return_obj);
die();
?>
MYCODE.JS
// this actually sends the AJAX request to the server.
function getUpdate() {
var jqXHR = $.ajax({
url : "ajax.php",
data : {
'func' : 'get_update',
'which_var' : 'num_people_logged_in'
},
dataType : 'json',
type : 'POST',
timeout : 10000
});
// attach 'promises' to the jqXHR object, which represents
// the AJAX call itself. 'promises' are, in this context,
// just events.
jqXHR.done(function(data,textStatus,jqXHR) {
// this executes if the AJAX call succeeded.
// the variable 'data' holds what the server
// sent us.
if ((data) && (data.request)) {
receiveUpdate(data.request);
}
});
jqXHR.fail(function(jqXHR,textStatus,errorThrown) {
// this executes if it failed
console.log("Fail: " + textStatus + " (" + errorThrown + ")");
});
jqXHR.always(function(a,textStatus,c){
// this executes either way, after .done or .fail
});
}
// this is called from jqXHR.done, on success
function receiveUpdate(request_obj) {
if (request_obj.num_people_logged_in) {
updateDOM(request_obj.num_people_logged_in);
}
}
function updateDOM(num_people_logged_in) {
if (num_people_logged_in) {
$("#mydiv > p.update").html("The updated value is: " + num_people_logged_in);
}
}
var timeoutID = null;
// setup our timer, to periodically make an
// AJAX call
function init() {
timeOutID = setInterval(function(){
getUpdate();
},5000);
}
// stop the timer
function cleanup() {
clearTimeout(timeoutID);
}
INDEX.HTML
<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<title>AJAX practice</title>
<!-- <link href="mycss.css" rel='stylesheet'> if needed -->
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script src="mycode.js"></script>
<script>
$(document).ready(function() {
init();
$("#cleanup").on("click",function(){
cleanup();
});
}); // end ready
</script>
</head>
<body>
<div id='mydiv'>
<p>
How many people are online?
</p>
<p class='update'>
</p>
</div>
<button id='cleanup'>Stop updating!</button>
</div>
</body>
</html>
下面的答案给你一个良好的开端。你也可以使用一个包装这个功能的JavaScript库。看看这个熟悉 - http://api.jquery.com/load/ – JohnP