Mobl is control-based. From what I can tell, I can't do arbitrary (javascript) logic on the DOM unless it is wrapped in a control.

right, well you can also do that from any piece of logic using the JQuery API, if you have to: http://docs.mobl-lang.org/mobl/JQuery

That example has the logic being performed from an event callback. How can I perform logic when a control is created? For example, I want to insert some html div into the DOM, then instantiate some jquery plugin on the inserted div. I have tried this and the compiler complained. I'm sure I'm doing it wrong but the documentation doesn't help. For example

screen root() {

  header("Title")

  $("#div").someplugin();

}

Can't do that. I tried to get around this by creating a control, but from what I can tell controls return html, not objects.

Not sure this is the place for it (maybe ask on the google group?) But there's two ways:

screen root() { mydiv@<div/> script { mydiv.someplugin(); } }

mydiv will be bound to a JQuery object representing the div. You can also just do this:

screen root() { script { $("#div").someplugin(); } }

So generally your answer is: put it in a script { ... } block.