Offer to insert an IIFE template in Custom HTML tags

It's good design to avoid inserting global persistent JS variables into the DOM
Then in many situations you could put your code into an IIFE and your variables vanish after the code has run

https://developer.mozilla.org/en-US/docs/Glossary/IIFE 

But it's a pain to type it in by heart
Offering to insert it would be nice

(function () {
    statements
})();