определение и инициализация

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
</head>
<body>
<script>
//a definition
var val0;
//an initialization
val0 = 5;
document.write(val0 + '<br />');
//a definition and an initialization
var val1 = 10;
document.write(val1 + '<br />');
//a definition and a dynamic initialization
var val2 = val0 + val1;
document.write(val2 + '<br />');
//a definition and an initialization with the constructor
var val3 = new Number(20);
document.write(val3 + '<br />');
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
</head>
<body>
<script>
//a definition
var val0;
//an initialization
val0 = 5;
document.write(val0 + '<br />');
//a definition and an initialization
var val1 = 10;
document.write(val1 + '<br />');
//a definition and a dynamic initialization
var val2 = val0 + val1;
document.write(val2 + '<br />');
//a definition and an initialization with the constructor
var val3 = new Number(20);
document.write(val3 + '<br />');
</script>
</body>
</html>