Endless loop rendering component on ReactJs

Because that your posts is fetch async, I believe that when your UserPopover component execute it's componentWillMount, the props.userId is undefined, and then you call UsersStore.findUser(this.props.userId), In UserStore, the getUser is called because it can't find user in local storage.

NOTE that every time the getUser's ajax finished, it trigger. So the UserPopover component execute onChange function, and call UsersStore.findUser again. That's a endless loop.

Please add a console.log(this.props.userId) in the UserPopover's componentWillMount to find out if it is like what i said above. I actually not 100% sure it.

That is a problem that all UserPopover instance share the same UserStore, I think we should rethink the structure of these components and stores. But I haven't thought out the best way yet.

You can do it like this:

TimelineComponent   |--PostComponent   |--UserPopover

UserPopover just listen for changes and update itself.

UserPopover listens for change at store, which holds which user's data should be in popover and on change updates itself. You can send also coordinates where to render. No need to create Popover for each Post.