itch.io

Its semi complicated and I'm not sure it does much so I tend not to bother giving the option to Exit or Quit with WebGL.
They can just navigate away from the page....

It is actually pretty simple. Make your exit text a button and add this code into your main menu script: 

public void QuitGame()

    {

        Application.Quit();

    }

Add the on click feature in unity then press the down arrow next to it then a name of your script you put it into will appear mine was "MainMenu" Then press the button that should say QuitGame() 

Also I forgot to mention. I would add a Main Menu object to add your main menu script. I am not 100% sure but I think it won't work unless you do this. 

I hope this helped! If you have any questions please ask!