how to use sessions with javascript code example

Example 1: javascript sessionStorage

var setsession = window.sessionStorage.setItem("animals", "cat");
	var getsession = window.sessionStorage.getItem("animals");
	console.log(getsession);

Example 2: set a value in session using javascript

<script type="text/javascript">
    function GetUserName()
    {

        var username = '<%= Session["UserName"] %>';
        alert(username );
    }
</script>