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