Comments
JavaScript uses C-style comments for both single-line and block comments.
A single-line comment begins with two forward-slash characters: //single line comment
<!DOCTYPE HTML>
<html>
<head>
<title>Example</title>
<script type="text/javascript">
// var firseName = 'firseName';
</script>
</head>
<body>
</body>
</html>
A block comment begins with a forward slash and asterisk (/*) and ends with the opposite (*/):
/*
* This is a multi-line
* Comment
*/
<!DOCTYPE HTML>
<html>
<head>
<title>Example</title>
<script type="text/javascript">
/* var firseName = 'firseName';
var thisIsAnotherVariable = 'this Is Another Variable';
document.writeln(firseName);
document.writeln(thisIsAnotherVariable);
*/
</script>
</head>
<body>
</body>
</html>