onMount
Note: This should only be set in the context of MountSpec. Will be ignored for LayoutSpec types.
Return
If this is true and this MountSpec is pureRender the mount process will check shouldComponentUpdate before unmounting/mounting in place and only update the content if necessary. If this is false instead, the mount process will only rely on the information provided by the layout process. As a rule of thumb this should only be set to true when for a Component the cost of calling Mount/Unmount greatly exceeds the cost of calling ShouldUpdate.
Deprecated
this param is ignored. MountSpecs with pureRender will now always check shouldUpdate on the main thread if the information from layout isn't able to be used.