One of the essential parts of a Meteor app is data and subscription management. In the past, we invoked subscriptions in the router itself and manage data inside it. However, now we consider that to be an anti-pattern.
In the client side, we've no control on when data will be available for the app. You need to wait for subscription to send the data.
- Router needs to wait for data and it needs to be reactive. This leads to a lot of unpredictable behavior specially when your app became larger.
- While data are loading, we may need to show loading messages. So we would need to find ways to interact with the router and the rendering layers. Showing a global loader is not a good pattern.
- Now, wherever you reuse the template, you need to define data requirement for that in the router again.
Moving subscription management to the template/component layer is the correct way. Then we've the flexibility to show and hide views based on the state of the subscription. We can also re-use templates in different places and we don't need to define how to pass data into them.
For Blaze, we can use template-level subscriptions. For React, we can directly use subscriptions. We can also use SubsManager to improve subscription performance. We'll discuss all of these in this section.
FlowRouter 1.x comes with its own subscription registration API. It's much better than managing subscriptions at the router level. Anyway, we are removing it in 3.x.
We don't remove it in 2.x because it's the one of the easiest way to enable FastRender for Blaze.