blueslip: Show popups for thrown non-Error values in development.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/blueslip.ts

@@ -111,7 +111,7 @@ export function error(msg: string, more_info?: object | undefined, original_erro
 if (DEVELOPMENT) {
     $(window).on("error", (event: JQuery.TriggeredEvent) => {
         const {originalEvent} = event;
-        if (originalEvent instanceof ErrorEvent && originalEvent.error instanceof Error) {
+        if (originalEvent instanceof ErrorEvent) {
             void display_stacktrace(originalEvent.error);
         }
     });

web/src/blueslip_stacktrace.ts

@@ -109,10 +109,26 @@ async function get_context(location: StackFrame): Promise<NumberedLine[] | undef
     }));
 }
 
-export async function display_stacktrace(ex: Error): Promise<void> {
+export async function display_stacktrace(ex: unknown): Promise<void> {
     const errors = [];
-    while (true) {
-        const stackframes: CleanStackFrame[] = await Promise.all(
+    do {
+        if (!(ex instanceof Error)) {
+            const prototype: unknown = Object.getPrototypeOf(ex);
+            errors.push({
+                name:
+                    typeof prototype === "object" &&
+                    prototype !== null &&
+                    "constructor" in prototype
+                        ? `thrown ${prototype.constructor.name}`
+                        : "thrown",
+                message: String(ex),
+                stackframes: [],
+            });
+            break;
+        }
+        const stackframes: CleanStackFrame[] =
+            ex instanceof Error
+                ? await Promise.all(
                       ErrorStackParser.parse(ex).map(async (location: StackFrame) => {
                           try {
                               location = await stack_trace_gps.getMappedLocation(location);
@@ -127,23 +143,20 @@ export async function display_stacktrace(ex: Error): Promise<void> {
                               context: await get_context(location),
                           };
                       }),
-        );
+                  )
+                : [];
         let more_info: string | undefined;
         if (ex instanceof BlueslipError) {
             more_info = JSON.stringify(ex.more_info, null, 4);
         }
         errors.push({
+            name: ex.name,
             message: exception_msg(ex),
             more_info,
             stackframes,
         });
-
-        if (ex.cause !== undefined && ex.cause instanceof Error) {
         ex = ex.cause;
-        } else {
-            break;
-        }
-    }
+    } while (ex !== undefined);
 
     const $alert = $("<div>").addClass("stacktrace").html(render_blueslip_stacktrace({errors}));
     $(".alert-box").append($alert);

web/templates/blueslip_stacktrace.hbs

@@ -3,7 +3,7 @@
         <div class="warning-symbol">
             <i class="fa fa-exclamation-triangle"></i>
         </div>
-        <div class="message"><strong>Error:</strong> {{ message }}</div>
+        <div class="message">{{#unless @first}}caused by {{/unless}}<strong>{{name}}:</strong> {{ message }}</div>
         {{#if @first}}
             <div class="exit"></div>
         {{/if}}