Javascript 中setTimeout 和 setInterval

這篇文章裏我們看一下javascript 中的如何使用setTimeout(), clearTimeout(), setInterval() 和 clearInterval() 幾個與時間設置有關的函數。使用這些函數可以設置定時器和延時任務，並且很方便。

• setTimeout()

windows.setTimeout()函數允許設定一定的延時，來執行所要執行的任務。設置的任務將在函數被調用後的數秒之後被執行。調用方法如下：

setTimeout ( expression, timeout );

expression  是到達延時時間後要執行的javascript 代碼

setTimeout 函數將返回數字類型的延時標誌，這個返回值會被clearTimeout函數調用 

簡單的例子：

 

<input type="button" name="clickMe" value="Click me and wait!"
onclick="setTimeout('alert(\'Surprise!\')', 5000)"/>

 

再點擊按鈕5秒後彈出信息："Surprise!"

 

一個較完整的例子：

<script type="text/javascript">

function setToRed ( )
{
  document.getElementById("colourButton").style.color = "#FF0000";
  setTimeout ( "setToBlack()", 2000 );
}

function setToBlack ( )
{
  document.getElementById("colourButton").style.color = "#000000";
}

</script>

<input type="button" name="clickMe" id="colourButton" value="Click me and wait!" onclick="setToRed()"/>

 

從上面的例子可以看到，按鈕被點擊後，按鈕文字變成紅色持續兩秒鐘，隨後變成黑色字體。

 

<script type="text/javascript">

var alertTimerId = 0;

function alertTimerClickHandler ( )
{
  if ( document.getElementById("alertTimerButton").value == "Click me and wait!" )
  {
    // Start the timer
    document.getElementById("alertTimerButton").value = "Click me to stop the timer!";
    alertTimerId = setTimeout ( "showAlert()", 3000 );
  }
  else
  {
    document.getElementById("alertTimerButton").value = "Click me and wait!";
    clearTimeout ( alertTimerId );
  }
}

function showAlert ( )
{
  alert ( "Too late! You didn't stop the timer." );
  document.getElementById("alertTimerButton").value = "Click me and wait!";
}

</script>

<input type="button" name="clickMe" id="alertTimerButton" value="Click me and wait!" onclick="alertTimerClickHandler()"/>

 

• clearTimeout()

 有的時候在延時程序完成之前要結束延時任務，會用到clearTimeout，其調用方式爲：

clearTimeout ( timeoutId );

timeoutId 是setTimeout函數被調用後返回的延時標誌

下面的例子當用戶點擊按鈕3秒鐘後，會彈出對話框信息，但是在此期間用戶可以再次點擊按鈕結束延時，阻止窗口的彈出。

 

 

<script type="text/javascript">

var alertTimerId = 0;

function alertTimerClickHandler ( )
{
  if ( document.getElementById("alertTimerButton").value == "Click me and wait!" )
  {
    // Start the timer
    document.getElementById("alertTimerButton").value = "Click me to stop the timer!";
    alertTimerId = setTimeout ( "showAlert()", 3000 );
  }
  else
  {
    document.getElementById("alertTimerButton").value = "Click me and wait!";
    clearTimeout ( alertTimerId );
  }
}

function showAlert ( )
{
  alert ( "Too late! You didn't stop the timer." );
  document.getElementById("alertTimerButton").value = "Click me and wait!";
}

</script>

<input type="button" name="clickMe" id="alertTimerButton" value="Click me and wait!" onclick="alertTimerClickHandler()"/>

 

• setInterval() 函數

和setTimeout()函數相似，setInterval函數的定義方法爲setInterval(expression, interval);當使用setTimeout函數做如下操作時，可以考慮用setInterval函數替換

 

setTimeout ( "doSomething()", 5000 );

function doSomething ( )
{
  // (do something here)
  setTimeout ( "doSomething()", 5000 );
}

 

 setInterval方法：

 

setInterval ( "doSomething()", 5000 );

function doSomething ( )
{
  // (do something here)
}

 

當需要提供連續精確的時間或時間間隔時setInterval將是最好的選擇

• clearInterval()

和clearTimeout函數一樣，通過setInterval返回的ID值，調用clearInterval方法結束一個setInterval,下面是一個可運行的setInterval和clearInterval函數簡單實例：

 

 

<script type="text/javascript">

var wooYayIntervalId = 0;

function wooYayClickHandler ( )
{
  if ( document.getElementById("wooYayButton").value == "Click me!" )
  {
    // Start the timer
    document.getElementById("wooYayButton").value = "Enough already!";
    wooYayIntervalId = setInterval ( "wooYay()", 1000 );
  }
  else
  {
    document.getElementById("wooYayMessage").innerHTML = "";
    document.getElementById("wooYayButton").value = "Click me!";
    clearInterval ( wooYayIntervalId );
  }
}

function wooYay ( )
{
  if ( Math.random ( ) > .5 )
  {
    document.getElementById("wooYayMessage").innerHTML = "Woo!";
  }
  else
  {
    document.getElementById("wooYayMessage").innerHTML = "Yay!";
  }

  setTimeout ( 'document.getElementById("wooYayMessage").innerHTML = ""', 500 );

}

</script>

<div id="wooYayMessage" style="height: 1.5em; font-size: 2em; color: red;"></div>
<input type="button" name="clickMe" id="wooYayButton" value="Click me!" onclick="wooYayClickHandler()"/>

 

 

 

 

 

 引用網址：http://www.elated.com/articles/javascript-timers-with-settimeout-and-setinterval/