window.setInterval() or setInterval()

setInterval() executes the code repeatedly at specific time intervals until the interval is canceled or the page is unloaded.

The setInterval() method accepts:

the code to execute
the milliseconds to wait between executions.

 
<!DOCTYPE HTML> 
<html> 
    <head> 
        <title>Example</title> 
    </head> 
    <body> 
        <script type="text/javascript"> 
            setInterval(function() { 
                document.writeln("Hello world!"); 
            }, 1000); 

        </script> 
    </body> 
</html>

Click to view the demo

The setInterval() method returns an interval ID. We can use the ID to cancel the interval with clearInterval() method.

 
<!DOCTYPE HTML> 
<html> 
    <head> 
        <title>Example</title> 
    </head> 
    <body> 
        <script type="text/javascript"> 
            var num = 0; 
            var max = 10; 
            var intervalId = null; 
            function incrementNumber() { 
                document.writeln(num++);
                //if the max has been reached, cancel all pending executions 
                if (num == max) { 
                    clearInterval(intervalId); 
                    document.writeln("Done"); 
                } 
            } 
            intervalId = setInterval(incrementNumber, 500); 


        </script> 
    </body> 
</html>

Click to view the demo