This method call fails in GJS:

    let props = chan.borrow_immutable_properties();

With:

    Error: No introspection information found for GStrv

GIR:

      <method name="borrow_immutable_properties"
              c:identifier="tp_channel_borrow_immutable_properties"
              doc="...">
        <return-value transfer-ownership="none" doc="a #GHashTable">
          <type name="GLib.HashTable" c:type="GHashTable*">
            <type name="utf8"/>
            <type name="GObject.Value"/>
          </type>
        </return-value>
      </method>

It's worth noting that other a{sv} GHashTables seem to work fine, I'm guessing it's that this one contains a GStrv.