          try:
              if self.binary or getattr(data, 'is_json_string', False):
                  if isinstance(data, bytes):
                      data = data.decode()
                  return json.loads(data)
              else:
                  json.dumps(data, cls=self.encoder)
          except (TypeError, ValueError):
              self.fail('invalid')
          return data
 
</s> remove             (postgres_fields and isinstance(model_field, postgres_fields.JSONField)):
 </s> add             (postgres_fields and isinstance(model_field, postgres_fields.JSONField)) or \
            (hasattr(models, 'JSONField') and isinstance(model_field, models.JSONField)): </s> remove         if postgres_fields and isinstance(model_field, postgres_fields.JSONField):
 </s> add         is_django_jsonfield = hasattr(models, 'JSONField') and isinstance(model_field, models.JSONField)
        if (postgres_fields and isinstance(model_field, postgres_fields.JSONField)) or is_django_jsonfield:
                return json.loads(data, cls=self.decoder)
          try:
              if self.binary or getattr(data, 'is_json_string', False):
                  if isinstance(data, bytes):
                      data = data.decode()
                return json.loads(data, cls=self.decoder)
              else:
                  json.dumps(data, cls=self.encoder)
          except (TypeError, ValueError):
              self.fail('invalid')
          return data
keep keep keep keep replace keep keep keep keep keep
 Add support for Django 3.1 JSONField (#7467)

Django 3.1 adds a new generic JSONField to replace the PostgreSQL-specific one. This adds support for the new field type, which should behave the same as the existing PostgreSQL field.

Django's new JSONField also includes support for a custom "decoder", so add support for that in the serializer field. 
rest_framework/fields.py