I am still getting the hang of D8... I have some entity types with various reference fields. I need to ajax in other values from another node type when changing the value of the entity reference select field I have.

Node type form 1:

    #####################################
    #  _____                            #
    # |Title|                           #
    #  ___________                      #
    # |Description|                     #
    #  _______________________________  #
    # |Node type 2 select reference |v| #
    #                                   #
    #####################################

Whenever I select a node from the *Node type 2 select reference* field I would like to ajax in a specific view mode of the node as `#suffix` markup. After selecting a node the resulting form should look like this:

    #####################################
    #  _____                            #
    # |Title|                           #
    #  ___________                      #
    # |Description|                     #
    #  _________________________        #
    # |Some node (node id: 2) |v|       #
    #                                   #
    #  * Node 2 value from field 'a'    #
    #  * Node 2 value from field 'b'    #
    #                                   #
    #####################################

I have attempted using `#ajax` property in a `hook_form_alter` on the select field but am not getting it to work due to errors. **What is the best approach here?**