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:
The setTimeout() method returns a value. In the syntax defined above, the value is stored in a variable called t. If you want to cancel the setTimeout() function, you can refer to it using the variable name.
The first parameter of setTimeout() can be a string of executable code, or a call to a function.
The second parameter indicates how many milliseconds from now you want to execute the first parameter.
Note: There are 1000 milliseconds in one second.
In the example below, when a button is clicked, the input field will start to count (for ever), starting at 0.
Notice that we also have a function that checks if the timer is already running, to avoid creating additional timers, if the button is pressed more than once:
<head>
<script type="text/javascript">
var c=0;
var t;
var timer_is_on=0;
function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}
function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}
function stopCount()
{
clearTimeout(t);
timer_is_on=0;
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!" onclick="doTimer()">
<input type="text" id="txt">
<input type="button" value="Stop count!" onclick="stopCount()">
</form>
</body>
</html>
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()
The setTimeout() Method
Syntax
| var t=setTimeout("javascript statement",milliseconds); |
The first parameter of setTimeout() can be a string of executable code, or a call to a function.
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 3 seconds. Example
|
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 a button is clicked, the input field will start to count (for ever), starting at 0.
Notice that we also have a function that checks if the timer is already running, to avoid creating additional timers, if the button is pressed more than once:
Example
|
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;
var timer_is_on=0;
function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}
function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}
function stopCount()
{
clearTimeout(t);
timer_is_on=0;
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!" onclick="doTimer()">
<input type="text" id="txt">
<input type="button" value="Stop count!" onclick="stopCount()">
</form>
</body>
</html>
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