使用JS是可以讓函數不直接執行的，而是在過了一個指定的時間間隔後才執行。這就叫做事件事件。
With JavaScript, it is possible to execute some code NOT immediately after a function is called, but after a specified time interval. This is called timing events.
使用JS是可以讓函數不直接執行的，而是在過了一個指定的時間間隔後才執行。這就叫做事件事件。
JavaScript Timing Events
JS時間事件
With JavaScript, it is possible to execute some code NOT immediately after a function is called, but after a specified time interval. This is called timing events.
使用JS是可以讓函數不直接執行的，而是在過了一個指定的時間間隔後才執行。這就叫做事件事件。
It's very easy to time events in JavaScript. The two key methods that are used are:
JS的時間事件是非常簡單的。使用了兩個關鍵的方法：
* setTimeout() - executes a code some time in the future
在一些時間後執行代碼
* clearTimeout() - cancels the setTimeout()
取消setTimeout()
Note: The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object.
注意：setTimeout() 和 Timeout() 都是HTML DOM Window 對象的方法。
setTimeout()
Syntax語法
var t=setTimeout("javascript statement",milliseconds)
The setTimeout() method returns a value - In the statement above, the value is stored in a variable called t. If you want to cancel this setTimeout(), you can refer to it using the variable name.
setTimeout()方法返回一個值 - 在上面的聲明裡，值被保存在變量t中。如果你想取消這個setTimeout()可以使用變量名來提出它（用clearTimeout(t)）
The first parameter of setTimeout() is a string that contains a JavaScript statement. This statement could be a statement like "alert('5 seconds!')" or a call to a function, like "alertMsg()".
setTomeout()的第一個參數是字符串聲明。它可以像"alert('5 seconds!')"或是調用一個函數像"alertMsg()"
The second parameter indicates how many milliseconds from now you want to execute the first parameter.
第二個參數用來表明從現在開始你希望在多少毫秒後執行第一個參數
Note: There are 1000 milliseconds in one second.
1000毫秒為一秒
Example
舉例
When the button is clicked in the example below, an alert box will be displayed after 5 seconds.
當下面的按鈕被點擊後，每過5秒就會出現一個警告框。
<html>
<head>
<script type="text/javascript">
function timedMsg()
{
var t=setTimeout("alert('5 seconds!')",5000)
}
</script>
</head>
<body>
<form>
<input type="button" value="Display timed alertbox!"
onClick="timedMsg()">
</form>
</body>
</html>
Example - Infinite Loop
無限循環
To get a timer to work in an infinite loop, we must write a function that calls itself. In the example below, when the button is clicked, the input field will start to count (for ever), starting at 0:
要得到一個無限循環的記時器，我們必須寫出一個自我調用的函數。下面的例子，當按鈕按下後，輸入框就會從0開始記數（永遠的）
<html>
<head>
<script type="text/javascript">
var c=0
var t
function timedCount()
{
document.getElementById('txt').value=c
c=c+1
t=setTimeout("timedCount()",1000)
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!"
onClick="timedCount()">
<input type="text" id="txt">
</form>
</body>
</html>
clearTimeout()
Syntax語法
clearTimeout(setTimeout_variable)
Example
舉例
The example below is the same as the "Infinite Loop" example above. The only difference is that we have now added a "Stop Count!" button that stops the timer:
下面的例子和上面的“無限循環”差不多。唯一的不同就是我們現在多了一個“停止記數”的按鈕來停止記時器。
<html>
<head>
<script type="text/javascript">
var c=0
var t
function timedCount()
{
document.getElementById('txt').value=c
c=c+1
t=setTimeout("timedCount()",1000)
}
function stopCount()
{
clearTimeout(t)
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!"
onClick="timedCount()">
<input type="text" id="txt">
<input type="button" value="Stop count!"
onClick="stopCount()">
</form>
</body>
</html>