id

js/script.js

function funMake() {
document.body.childNodes[2].id = 'p3';
}
window.onload = function() {
for(var i=1; i<=3; i++) {
document.getElementById('d1').innerHTML += '<h3>' + document.body.childNodes[i].id + '</h3>';
}
}

function funMake() {
document.body.childNodes[2].id = 'p3';
}
window.onload = function() {
for(var i=1; i<=3; i++) {
document.getElementById('d1').innerHTML += '<h3>' + document.body.childNodes[i].id + '</h3>';
}
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<p id="p1">Hello World!</p>
<p id="p2">Привет Мир!</p>
<p>To be or not to be?</p>
<div id="d1"></div>
<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="p1">Hello World!</p>
<p id="p2">Привет Мир!</p>
<p>To be or not to be?</p>
<div id="d1"></div>
<script>
funMake();
</script>
</body>
</html>