See this stack overflow question by someone else for a similar issue: http://stackoverflow.com/questions/28069808/meteor-call-js-after-dom-changed-by-reactive-template-data?noredirect=1#comment48987262_28069808
I have an app with a bunch of tabs. When a tab is selected, the corresponding section of body becomes visible by a reactive change to a HTML class. When this happens, I want to focus() a text input box. However, because the section of body was display: none, and because you can’t call focus on something that has display:none set, there is no right time for me to call focus().
The successful workaround is to put a setTimeout for 50ms in the code that makes the change to the session variable to cause the reactive change, but obviously that’s not the right way to do anything.