Nothing, kill it

So I wasnt going mad

(but if its not doing anything why did you spend your time converting it to es6?)

Actually I'm wrong here, the script will try to set the height of the iframe according to the contents inside it. Probably it shouldn't be useful as you can do that with css. So it's there for those that didn't actually styled correctly the iframe. In an perfect world that people used correctly HTML5 this should be redundant...

Actually I'm wrong here, the script will try to set the height of the iframe according to the contents inside it.

Doesnt seem to do that in my tests

Probably it shouldn't be useful as you can do that with css.

Really? I dont think you can but would like to learn

Doesnt seem to do that in my tests

Is the iframe in the same origin? Cross origin I think won't work anymore (although it's the iframe that shouldn't have right on the parent doc)

same origin

Do you have attribute load appended on the iframe?
Comes from here:

MY FAULT

I didnt set autoheight on