Javascript close window, if coming from other source, redirect

I am currently making one website, and i kind of need help. I'm currently using

< href='javascript:window.close();' class="btn btn-primary"> Close window > (its not in format here as i don't know how to but you get the idea and it worked so.

-script to Close opened window with a button, but i somehow need some sort of IF command to redirect the page to the front page from here, if you for some reason get there trough other source than going by the window. so how it works.

On the front page there's buttons which opens this window, and the button closes it... aand when coming from other source, it should redirect to frontpage I have been trying many different things but im still kind of new to this so thanks for answers beforehand!