Handle the render Event
When a component is rendered or rerendered, the aura:valueRender event, also known as the render event, is fired. Handle this event to perform
post-processing on the DOM or react to component rendering or rerendering. The event is
preferred and easier to use than the alternative of creating a custom
renderer.
The render event is fired after all methods in a custom renderer are invoked. For more details on the sequence in the rendering or rerendering lifecycles, see Create a Custom Renderer.
Handling the aura:valueRender event is similar to handling the init hook. Add a handler to your component's markup.
<aura:handler name="render" value="{!this}" action="{!c.onRender}"/>
In this example, the onRender action in your client-side controller handles initial rendering and rerendering of the component. You can choose any name for the action attribute.