使用setTimeout函数时遇到问题 [英] Trouble using setTimeout function
问题描述
我一直无法正确使用setTimeout函数，因此我尝试编写示例脚本来更新进度条，但是同样，它不起作用.而是在进度条更新为100％之前运行整个程序.有人可以看一下这段代码，然后告诉我我在做什么错吗?
I've never been able to properly use the setTimeout function, so I tried writing a sample script to update a progress bar, but again, it does not work. Instead, the entire program runs before the progress bar is updated to 100%. Would somebody be able to look at this code and tell me what I'm doing wrong?
我要使用的代码来自 http://digitalbush.com/projects/progress-bar-plugin/
谢谢！
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<script language="javascript" type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script>
<script src="http://digitalbush.com/wp-content/uploads/2007/02/jqueryprogressbar.js" type="text/javascript"></script>
<title>Progress Bar test</title>
</head>
<body>
<style>
/* progress bar container */
#progressbar{
border:1px solid black;
width:200px;
height:20px;
position:relative;
color:black;
}
/* color bar */
#progressbar div.progress{
position:absolute;
width:0;
height:100%;
overflow:hidden;
background-color:#369;
}
/* text on bar */
#progressbar div.progress .text{
position:absolute;
text-align:center;
color:white;
}
/* text off bar */
#progressbar div.text{
position:absolute;
width:100%;
height:100%;
text-align:center;
}
</style>
<div id="progressbar"></div>
<input type='button' value='start' onClick='run()' />
<script>
function run() {
for (i=0; i<100; i++) {
setTimeout( function() {
$("#progressbar").reportprogress(i);
}, 500);
}
}
</script>
</body>
</html>
推荐答案
问题在于变量i成为闭包的一部分，并且在执行函数时已经等于100.
The issue is that variable i becomes the part of the closure and, when the function is executed, is already equal to 100.
您当前使用的代码实际上会创建一百个引用同一变量(全局i)的超时.到执行所有功能时，i等于100，因此您将100作为当前进度报告为100.
The code you have currently literally creates a hundred of timeouts referencing the same variable(global i). By the time all of the functions are executed, i equals 100, therefore you report 100 as current progress 100 times.
正确的版本应如下所示:
The proper version should look like that:
function run() {
var i = 0;
setTimeout( function updateProgress() {
$("#progressbar").reportprogress(i++);
if (i < 100){
setTimeout(updateProgress, 500);
}
}, 500);
}
您可以检查javascript花园的闭包部分，以获取解释和可能的其他信息解决方案.
You could check closures part of javascript garden for explanation and possible other solutions.
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