How to do XMLHttpRequest PUT with query parameters?

Question

i've got a rest server that listens to PUT's with a pair of query params. The test cases of it's api uses a Jersey client and look like this :

 public void putV1ItemsIdShouldSaveNewObj() throws Exception {
        String json = new ObjectMapper().writeValueAsString(obj);
        itemsTarget = itemsTarget.queryParam("x",2);
        itemsTarget = itemsTarget.queryParam("y",2);
        Response r = itemsTarget.request().put(Entity.text(json));
        String jsonans = r.readEntity(String.class);
        assertThat(jsonans, is(not(nullValue())));
    }

How can I make this kind of puts with arguments in XMLHttpRequest ?

        req.open("PUT", "http://00.00.00.00:8080/PATH/obj?x=40&Y=50", true);
        req.send("{\"atr1\":\"aaaa\",\"atr2\":3}");

Appending to the target url is not working