OK. That makes sence. Perhaps I was a tad impatient. Sorry.
Before I decide to post a job request on Slack, I thought I would try a simpler solution, using http://tympanus.net/codrops/2014/02/06/fullscreen-overlay-effects/. Using the first example (index.html and demo1.js), I’m trying to get the trigger button to fadeout/fadein in relation with the closing cross in the triggered menu. I have wrapped the trigger button in a div.menuopen and also given the button a class .overlay-open.
Here I have just added menuopen = document.querySelector( 'div.menuopen' ), and classie.add( menuopen, 'open' ); to display the menu hamburger when clicking the closing cross. But, first the trigger button / hamburger icon must fadeout.