конкатенация

js/script.js

var str0 = 'Hello';
var str1 = ' ';
var str2 = 'World';
var str3 = '!';
var res = str0 + str1 + str2 + str3;
function funMake() {
document.write(res + '<br />');
}

var str0 = 'Hello';
var str1 = ' ';
var str2 = 'World';
var str3 = '!';
var res = str0 + str1 + str2 + str3;

function funMake() {
 document.write(res + '
');
}

index.html

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