Simple tracking for frontend js errors

app/lib/express.js

@@ -691,6 +691,20 @@ router.get("/debug-error", (_req, res) => {
   res.send("should never reach here");
 });
 
+router.post("/frontend-error", (req, res) => {
+  const message = req.body.message;
+  const stacktrace = req.body.stacktrace;
+
+  if (SENTRY_DSN && process.env.NODE_ENV == "production") {
+    Sentry.captureEvent({
+      message,
+      stacktrace,
+    });
+  }
+
+  res.send("ok");
+});
+
 router.get("/metrics", { public: true }, (_req, res) => {
   res.set("Content-Type", metrics.register.contentType);
   res.end(metrics.register.metrics());

app/public/js/shared.js

@@ -31,3 +31,30 @@ document.addEventListener("readystatechange", (event) => {
   }
 });
 setTimeout(fixImageHeights, 2000);
+
+/**
+ * Client JS error monitoring
+ */
+
+window.debugError = () => {
+  const throwLevel1 = () => {
+    throwLevel2();
+  };
+  const throwLevel2 = () => {
+    const object = {};
+    object.isUndefinedAFunction();
+  };
+  setTimeout(throwLevel1, 1);
+};
+
+window.onerror = (message, _url, _lineNo, _columnNo, error) => {
+  fetch("/frontend-error", {
+    method: "POST",
+    headers: { "Content-Type": "application/x-www-form-urlencoded" },
+    body:
+      "message=" +
+      encodeURIComponent(message.toString()) +
+      "&stacktrace=" +
+      encodeURIComponent(error.stack),
+  });
+};