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分享问一个jav的setTimeout的问题。（可能是语法方面概念混淆）
<script language="JavaScript">
function showtime () {
var now = new Date();
var hours = now.getHours();
var minutes = now.getMinutes();
var seconds = now.getSeconds()
var timeValue = "" + ((hours >12) ? hours -12 :hours)
timeValue += ((minutes < 10) ? ":0" : ":") + minutes
timeValue += ((seconds < 10) ? ":0" : ":") + seconds
timeValue += (hours >= 12) ? " P.M." : " A.M."
document.all.item("aa").value = timeValue;
timerID = setTimeout("showtime()",1000);
timerRunning = true;
}
问题：timerID = setTimeout("showtime()",1000);是一个递归调用吗？
</script>
function showtime () {
var now = new Date();
var hours = now.getHours();
var minutes = now.getMinutes();
var seconds = now.getSeconds()
var timeValue = "" + ((hours >12) ? hours -12 :hours)
timeValue += ((minutes < 10) ? ":0" : ":") + minutes
timeValue += ((seconds < 10) ? ":0" : ":") + seconds
timeValue += (hours >= 12) ? " P.M." : " A.M."
document.all.item("aa").value = timeValue;
timerID = setTimeout("showtime()",1000);
timerRunning = true;
}
问题：timerID = setTimeout("showtime()",1000);是一个递归调用吗？
</script>
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zzmdegm 2006-01-11
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up
lovefootball 2006-01-10
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????
zzmdegm 2006-01-10
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up
zzmdegm 2006-01-07
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setTimeout method
Evaluates an expression after a specified number of milliseconds have elapsed.
语法
timeoutID=setTimeout(expression, msec)
timeoutID is an identifier that is used only to cancel the evaluation with the clearTimeout method.
expression is a string expression or a property of an existing object.
msec is a numeric value, numeric string, or a property of an existing object in millisecond units.
方法
frame, window
描述
The setTimeout method evaluates an expression after a specified amount of time. It does not evaluate the expression repeatedly. For example, if a setTimeout method specifies 5 seconds, the expression is evaluated after 5 seconds, not every 5 seconds.
例子
Example 1. The following example displays an alert message 5 seconds (5,000 milliseconds) after the user clicks a button. If the user clicks the second button before the alert message is displayed, the timeout is canceled and the alert does not display.
<SCRIPT LANGUAGE="JavaScript">
function displayAlert() {
alert("5 seconds have elapsed since the button was clicked.")
}
</SCRIPT>
<BODY>
<FORM>
Click the button on the left for a reminder in 5 seconds;
click the button on the right to cancel the reminder before
it is displayed.
<P>
<INPUT TYPE="button" VALUE="5-second reminder"
NAME="remind_button"
onClick="timerID=setTimeout('displayAlert()',5000)">
<INPUT TYPE="button" VALUE="Clear the 5-second reminder"
NAME="remind_disable_button"
onClick="clearTimeout(timerID)">
</FORM>
</BODY>
Example 2. The following example displays the current time in a text object. The showtime() function, which is called recursively, uses the setTimeout method update the time every second.
<HEAD>
<SCRIPT LANGUAGE="JavaScript">
<!--
var timerID = null
var timerRunning = false
function stopclock(){
if(timerRunning)
clearTimeout(timerID)
timerRunning = false
}
function startclock(){
// Make sure the clock is stopped
stopclock()
showtime()
}
function showtime(){
var now = new Date()
var hours = now.getHours()
var minutes = now.getMinutes()
var seconds = now.getSeconds()
var timeValue = "" + ((hours > 12) ? hours - 12 : hours)
timeValue += ((minutes < 10) ? ":0" : ":") + minutes
timeValue += ((seconds < 10) ? ":0" : ":") + seconds
timeValue += (hours >= 12) ? " P.M." : " A.M."
document.clock.face.value = timeValue
timerID = setTimeout("showtime()",1000)
timerRunning = true
}
//-->
</SCRIPT>
</HEAD>
<BODY onLoad="startclock()">
<FORM NAME="clock" onSubmit="0">
<INPUT TYPE="text" NAME="face" SIZE=12 VALUE ="">
</FORM>
</BODY>
相关
clearTimeout method
Evaluates an expression after a specified number of milliseconds have elapsed.
语法
timeoutID=setTimeout(expression, msec)
timeoutID is an identifier that is used only to cancel the evaluation with the clearTimeout method.
expression is a string expression or a property of an existing object.
msec is a numeric value, numeric string, or a property of an existing object in millisecond units.
方法
frame, window
描述
The setTimeout method evaluates an expression after a specified amount of time. It does not evaluate the expression repeatedly. For example, if a setTimeout method specifies 5 seconds, the expression is evaluated after 5 seconds, not every 5 seconds.
例子
Example 1. The following example displays an alert message 5 seconds (5,000 milliseconds) after the user clicks a button. If the user clicks the second button before the alert message is displayed, the timeout is canceled and the alert does not display.
<SCRIPT LANGUAGE="JavaScript">
function displayAlert() {
alert("5 seconds have elapsed since the button was clicked.")
}
</SCRIPT>
<BODY>
<FORM>
Click the button on the left for a reminder in 5 seconds;
click the button on the right to cancel the reminder before
it is displayed.
<P>
<INPUT TYPE="button" VALUE="5-second reminder"
NAME="remind_button"
onClick="timerID=setTimeout('displayAlert()',5000)">
<INPUT TYPE="button" VALUE="Clear the 5-second reminder"
NAME="remind_disable_button"
onClick="clearTimeout(timerID)">
</FORM>
</BODY>
Example 2. The following example displays the current time in a text object. The showtime() function, which is called recursively, uses the setTimeout method update the time every second.
<HEAD>
<SCRIPT LANGUAGE="JavaScript">
<!--
var timerID = null
var timerRunning = false
function stopclock(){
if(timerRunning)
clearTimeout(timerID)
timerRunning = false
}
function startclock(){
// Make sure the clock is stopped
stopclock()
showtime()
}
function showtime(){
var now = new Date()
var hours = now.getHours()
var minutes = now.getMinutes()
var seconds = now.getSeconds()
var timeValue = "" + ((hours > 12) ? hours - 12 : hours)
timeValue += ((minutes < 10) ? ":0" : ":") + minutes
timeValue += ((seconds < 10) ? ":0" : ":") + seconds
timeValue += (hours >= 12) ? " P.M." : " A.M."
document.clock.face.value = timeValue
timerID = setTimeout("showtime()",1000)
timerRunning = true
}
//-->
</SCRIPT>
</HEAD>
<BODY onLoad="startclock()">
<FORM NAME="clock" onSubmit="0">
<INPUT TYPE="text" NAME="face" SIZE=12 VALUE ="">
</FORM>
</BODY>
相关
clearTimeout method
zzmdegm 2006-01-07
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window对象有两个主要的定时方法，分别是setTimeout 和 setInteval 他们的语法基本上相同，但是完成的功能取有区别。
setTimeout方法是定时程序，也就是在什么时间以后干什么。干完了就拉倒。
setInterval方法则是表示间隔一定时间反复执行某操作。
如果用setTimeout实现setInerval的功能，就需要在执行的程序中再定时调用自己才行。如果要清除计数器需要 根据使用的方法不同，调用不同的清除方法：
例如：tttt=setTimeout('northsnow()',1000);
clearTimeout(tttt);
或者：
tttt=setInterval('northsnow()',1000);
clearInteval(tttt);
举一个例子：
<div id="liujincai"></div>
<input type="button" name="start" value="start" onclick='startShow();'>
<input type="button" name="stop" value="stop" onclick="stop();">
<script language="javascript">
var intvalue=1;
var timer2=null;
function startShow()
{
liujincai.innerHTML=liujincai.innerHTML + " " + (intvalue ++).toString();
timer2=window.setTimeout("startShow()",2000);
}
function stop()
{
window.clearTimeout(timer2);
}
</script>
或者：
<div id="liujincai"></div>
<input type="button" name="start" value="start" onclick='timer2=window.setInterval("startShow()",2000);//startShow();'>
<input type="button" name="stop" value="stop" onclick="stop();">
<script language="javascript">
var intvalue=1;
var timer2=null;
function startShow()
{
liujincai.innerHTML=liujincai.innerHTML + " " + (intvalue ++).toString();
}
function stop()
{
window.clearInterval(timer2);
}
</script>
setTimeout方法是定时程序，也就是在什么时间以后干什么。干完了就拉倒。
setInterval方法则是表示间隔一定时间反复执行某操作。
如果用setTimeout实现setInerval的功能，就需要在执行的程序中再定时调用自己才行。如果要清除计数器需要 根据使用的方法不同，调用不同的清除方法：
例如：tttt=setTimeout('northsnow()',1000);
clearTimeout(tttt);
或者：
tttt=setInterval('northsnow()',1000);
clearInteval(tttt);
举一个例子：
<div id="liujincai"></div>
<input type="button" name="start" value="start" onclick='startShow();'>
<input type="button" name="stop" value="stop" onclick="stop();">
<script language="javascript">
var intvalue=1;
var timer2=null;
function startShow()
{
liujincai.innerHTML=liujincai.innerHTML + " " + (intvalue ++).toString();
timer2=window.setTimeout("startShow()",2000);
}
function stop()
{
window.clearTimeout(timer2);
}
</script>
或者：
<div id="liujincai"></div>
<input type="button" name="start" value="start" onclick='timer2=window.setInterval("startShow()",2000);//startShow();'>
<input type="button" name="stop" value="stop" onclick="stop();">
<script language="javascript">
var intvalue=1;
var timer2=null;
function startShow()
{
liujincai.innerHTML=liujincai.innerHTML + " " + (intvalue ++).toString();
}
function stop()
{
window.clearInterval(timer2);
}
</script>
