diff --git a/DESCRIPTION b/DESCRIPTION
index 7262138..c9d5eb7 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: xaringan
 Type: Package
 Title: Presentation Ninja
-Version: 0.28.1
+Version: 0.28.2
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666")),
     person(given = "Posit Software, PBC", role = c("cph", "fnd")),
@@ -46,13 +46,14 @@ Depends: R (>= 3.5.0)
 Imports:
     htmltools,
     knitr (>= 1.30),
-    servr (>= 0.13),
+    servr (>= 0.28.2),
     xfun (>= 0.18),
     rmarkdown (>= 2.8)
-Suggests: rstudioapi, testit
+Suggests: rstudioapi, jsonlite, testit
 License: MIT + file LICENSE
 URL: https://github.com/yihui/xaringan
 BugReports: https://github.com/yihui/xaringan/issues
 VignetteBuilder: knitr
 Encoding: UTF-8
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.1
+Remotes: yihui/servr
diff --git a/NEWS.md b/NEWS.md
index 58ee5f0..f5af46f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # CHANGES IN xaringan VERSION 0.29
 
+- Internal changes for `xaringan::inf_mr()` according to changes in the **servr** package.
 
 # CHANGES IN xaringan VERSION 0.28
 
diff --git a/R/render.R b/R/render.R
index 50c9ea9..92682df 100644
--- a/R/render.R
+++ b/R/render.R
@@ -323,6 +323,7 @@ infinite_moon_reader = function(moon, cast_from = '.', ...) {
         if (!r || missing(message)) return(FALSE)
         ctx = rstudioapi::getSourceEditorContext()
         if (identical(normalize_path(as.character(ctx[['path']])), moon)) {
+          if (is.character(message)) message = jsonlite::fromJSON(message)
           if (isTRUE(message[['focused']])) {
             # auto-navigate to the slide source corresponding to current HTML
             # page only when the slides are on focus
diff --git a/inst/rmarkdown/templates/xaringan/resources/js/ws-handler.js b/inst/rmarkdown/templates/xaringan/resources/js/ws-handler.js
index b907241..fe1e4bc 100644
--- a/inst/rmarkdown/templates/xaringan/resources/js/ws-handler.js
+++ b/inst/rmarkdown/templates/xaringan/resources/js/ws-handler.js
@@ -1,37 +1,41 @@
-var flag, focused = false;
-ws.onmessage = function(event) {
+((interval, path) => {
+const ws = new WebSocket(location.href.replace(/^http/, 'ws').replace(/\/?$/, '/websocket/'));
+let flag, focused = false;
+
+window.addEventListener('focus', e => { focused = true; });
+window.addEventListener('blur',  e => { focused = false; });
+
+ws.onmessage = event => {
   flag = true;
-  var d = JSON.parse(event.data);
+  const d = JSON.parse(event.data);
   if (d === true) {
     // fire a servr:reload event
     Event && document.dispatchEvent(new Event('servr:reload'));
     return location.reload();
   }
   if (!window.slideshow || !window.remark || d === false || d === null) return;
-  var p = d.page; if (p < 1) p = 1;
+  let p = d.page; if (p < 1) p = 1;
   if (!focused) slideshow.gotoSlide(p);
   if (d.markdown === false) return;
-  var el = document.getElementsByClassName('remark-slides-area');
+  let el = document.getElementsByClassName('remark-slides-area');
   el = el[0].children[p - 1].querySelector('.remark-slide-content');
-  var n = el.querySelector('.remark-slide-number').outerHTML.toString();
+  const n = el.querySelector('.remark-slide-number').outerHTML.toString();
   el.innerHTML = remark.convert(d.markdown) + n;
   if (window.MathJax) {
     slideshow._releaseMath(el);
     MathJax.Hub.Queue(['Typeset', MathJax.Hub, el]);
   }
-  var i, code, codes = el.getElementsByTagName('pre');
-  for (i = 0; i < codes.length; i++) {
-    code = codes[i];
+  [...el.getElementsByTagName('pre')].forEach(code => {
     if (code.querySelector('.\\.hidden')) {
-      code.style.display = 'none'; continue;
+      code.style.display = 'none'; return;
     }
-    remark.highlighter.engine.highlightBlock(codes[i]);
-  }
+    remark.highlighter.engine.highlightBlock(code);
+  });
 };
 
 // send the page number to R, so RStudio can move to the Rmd source of the
 // current slide
-setInterval(function() {
+setInterval(() => {
   if (flag === false || ws.readyState !== ws.OPEN) return;
   flag = false;
   ws.send((window.slideshow && window.remark) ? JSON.stringify({
@@ -39,7 +43,5 @@ setInterval(function() {
     'N': slideshow.getSlideCount(),
     'focused': focused
   }) : '{}');
-}, !!SERVR_INTERVAL);
-
-window.addEventListener('focus', function(e) { focused = true; });
-window.addEventListener('blur',  function(e) { focused = false; });
+}, interval);
+})