See my question here: https://forum.mendix.com/link/questions/110016.
Currently, there appears to be no way for me to check the type of the attributes when they are passed to my React component. The type is returned for an attribute that is connected to a datasource. But, for non-datasource attributes, this information is not provided. I have scoured the JSON objects provided by the Mendix system for a way to do this, but there is simply no bridge to obtain this information for each type of attribute.
Please include the type of attribute in the JSON object, just like what is done for datasource attributes. (Picture example is available in my question above).