Create an object of window.open() and then pass the function into document.write() method to pass JavaScript function value into a new tab.
object.document.write(function);Open New Tab with Results from JavaScript function examples
HTML example codes:-
Add 2 numbers and pass to result into another tab
<html>
<body>
	<script>
		function msg(a, b){
			return a+b;
		}
		
		var winPrint = window.open('', '', width=800,height=600,toolbar=0);
		winPrint.document.write( msg(1,2));	
	</script>
</body>
</html>

Show String message into another tab using JS function
<html>
<body>
	<script>
		function msg(mark){
			if (mark>40){
				return "Hello Wrold"
			}
		}
		var winPrint = window.open('', '', width=800,height=600,toolbar=0);
		winPrint.document.write(msg(200));	
	</script>
</body>
</html>
Output:

Do comment if you have any doubts and suggestions on this JS function topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version