setTimeout()

js/script.js

function funString() {
var str = 'Hello World!';
document.getElementById('p').innerHTML = str;
}
function funMake() {
setTimeout ('funString()', 2000);
}

function funString() {
var str = 'Hello World!';
document.getElementById('p').innerHTML = str;
}
function funMake() {
setTimeout ('funString()', 2000);
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<p id="p"></p>
<script>
funMake();
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<p id="p"></p>
<script>
funMake();
</script>
</body>
</html>