JavaScript Timing Events
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Timing Events
Thewindow object allows execution of code at specified time intervals.
These time intervals are called timing events.
The two key methods to use with JavaScript are:
setTimeout(function, milliseconds)
Executes a function, after waiting a specified number of milliseconds.setInterval(function, milliseconds)
Same as setTimeout(), but repeats the execution of the function continuously.
ThesetTimeout() andsetInterval() are both methods of the HTML DOM Window object.
The setTimeout() Method
Thewindow.setTimeout() method can be written without the window prefix.
The first parameter is a function to be executed.
The second parameter indicates the number of milliseconds before execution.
Example
Click a button. Wait 3 seconds, and the page will alert "Hello":
<script>
function myFunction() {
alert('Hello');
}
</script>
How to Stop the Execution?
TheclearTimeout() method stops the execution of the function specified in setTimeout().
Thewindow.clearTimeout() method can be written without the window prefix.
TheclearTimeout() method uses the variable returned fromsetTimeout():
clearTimeout(myVar);
If the function has not already been executed, you can stop the execution by calling theclearTimeout() method:
Example
Same example as above, but with an added "Stop" button:
<button onclick="clearTimeout(myVar)">Stop it</button>
The setInterval() Method
ThesetInterval() method repeats a given function at every given time-interval.
Thewindow.setInterval() method can be written without the window prefix.
The first parameter is the function to be executed.
The second parameter indicates the length of the time-interval between each execution.
This example executes a function called "myTimer" once every second (like a digital watch).
Example
Display the current time:
function myTimer() {
const d = new Date();
document.getElementById("demo").innerHTML = d.toLocaleTimeString();
}
There are 1000 milliseconds in one second.
How to Stop the Execution?
TheclearInterval() method stops the executions of the function specified in the setInterval() method.
Thewindow.clearInterval() method can be written without the window prefix.
TheclearInterval() method uses the variable returned fromsetInterval():
clearInterval(myVar);
Example
Same example as above, but we have added a "Stop time" button:
<button onclick="clearInterval(myVar)">Stop time</button>
<script>
let myVar = setInterval(myTimer, 1000);
function myTimer() {
const d = new Date();
document.getElementById("demo").innerHTML = d.toLocaleTimeString();
}
</script>
More Examples
A clock created with a timing event
