Added built-in noVNC support.

public/novnc/app/error-handler.js

@@ -0,0 +1,58 @@
+// NB: this should *not* be included as a module until we have
+// native support in the browsers, so that our error handler
+// can catch script-loading errors.
+
+// No ES6 can be used in this file since it's used for the translation
+/* eslint-disable prefer-arrow-callback */
+
+(function _scope() {
+    "use strict";
+
+    // Fallback for all uncought errors
+    function handleError(event, err) {
+        try {
+            const msg = document.getElementById('noVNC_fallback_errormsg');
+
+            // Only show the initial error
+            if (msg.hasChildNodes()) {
+                return false;
+            }
+
+            let div = document.createElement("div");
+            div.classList.add('noVNC_message');
+            div.appendChild(document.createTextNode(event.message));
+            msg.appendChild(div);
+
+            if (event.filename) {
+                div = document.createElement("div");
+                div.className = 'noVNC_location';
+                let text = event.filename;
+                if (event.lineno !== undefined) {
+                    text += ":" + event.lineno;
+                    if (event.colno !== undefined) {
+                        text += ":" + event.colno;
+                    }
+                }
+                div.appendChild(document.createTextNode(text));
+                msg.appendChild(div);
+            }
+
+            if (err && err.stack) {
+                div = document.createElement("div");
+                div.className = 'noVNC_stack';
+                div.appendChild(document.createTextNode(err.stack));
+                msg.appendChild(div);
+            }
+
+            document.getElementById('noVNC_fallback_error')
+                .classList.add("noVNC_open");
+        } catch (exc) {
+            document.write("noVNC encountered an error.");
+        }
+        // Don't return true since this would prevent the error
+        // from being printed to the browser console.
+        return false;
+    }
+    window.addEventListener('error', function onerror(evt) { handleError(evt, evt.error); });
+    window.addEventListener('unhandledrejection', function onreject(evt) { handleError(evt.reason, evt.reason); });
+})();