Insert JS in widget or dashboard

[Elko29]

Hi, thank you for your great work !
It's not a bug report but only a question.

I use Mozaik V1 and I want to refresh automatically an Iframe in a widget. I use mozaik-ext-embed, to create and use iframe no problem but I don't know how to insert some JS to reload periodically my Iframe ...

Is there a way to add javascript to a widget or to the entire dashboard?

Thanks !
Alex.