code: function render(vm) {
  	var observerData = vm._mobxObserver,
  		that = this,
  		args = arguments,
  		result;
  
  	// If vm was unmounted and is now being reused:
  	if (!observerData.reaction)
  		setReaction(vm);
  
  	// Note: the following is allowed to run by MobX even if the reaction is not stale:
  	observerData.reaction.track(function() {
  		mobx._allowStateChanges(false, function() {
  			result = observerData.render.apply(that, args);
  		});
  	});
  	observerData.stale = false;
  
  	return result;
  }
docs: The render() wrapper assigned to each observer vm: