document.getElementById('message').innerHTML = 'Hello';
<!DOCTYPE html>
<html>
<head>
<title>Js</title>
<meta charset="utf-8">
<script src="js/java_script.js"> </script>
</head>
<body>
<div id="message"></div>
</body>
</html>
<head>
<title>Js</title>
<meta charset="utf-8">
</head>
<body>
<div id="message"></div>
<script src="js/java_script.js"> </script>
</body>
</html>
document.addEventListener('DOMContentLoaded', function() {
document.getElementById('message').innerHTML = 'Hello';
}, false);