Returns the root DOM node of a mounted component.

Force re-rendering of all mounted Reagent components. This is
probably only useful in a development environment, when you want to
update components in response to some dynamic changes to code.

Note that force-update-all may not update root components. This
happens if a component 'foo' is mounted with `(render [foo])` (since
functions are passed by value, and not by reference, in
ClojureScript). To get around this you'll have to introduce a layer
of indirection, for example by using `(render [#'foo])` instead.

Render a Reagent component into the DOM. The first argument may be
either a vector (using Reagent's Hiccup syntax), or a React element. The second argument should be a DOM node.

Optionally takes a callback that is called when the component is in place.

Returns the mounted component instance.