Blog : JavaScript Timing Events

JavaScript Timing Events

JavaScript Timing Events
With JavaScript, it is possible to execute some code after a specified time-interval. This is called timing events.

It's very easy to time events in JavaScript. The two key methods that are used are:

setTimeout() - executes a code some time in the future
clearTimeout() - cancels the setTimeout()
Note: The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object.


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The setTimeout() Method
Syntax
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.

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()".

The second parameter indicates how many milliseconds from now you want to execute the first parameter.

Note: There are 1000 milliseconds in one second.

Example
When the button is clicked in the example below, an alert box will be displayed after 5 seconds.

Example
<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
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:

Example
<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>

 


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The clearTimeout() Method
Syntax
clearTimeout(setTimeout_variable)

Example
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:

Example
<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>