fix(docs-infra): correctly handle reported errors (#42883)

Error-handling in AIO happens mainly in two places:
1. For errors happening inside the app we have a custom `ErrorHandler`
   implementation, `ReportingErrorHandler`. `ReportingErrorHandler`
   passes errors to the default `ErrorHandler` (for them to be logged to
   the console) and also forwards them to `window.onerror()`.
2. Errors happening outside the app and errors forwarded by
   `ReportingErrorHandler` are handled by `window.onerror()`, which in
   turn reports them to Google analytics.

Previously, we were making some assumptions (which turned out to be
incorrect based on the info captured in Google analytics - see #28106):
- `ReportingErrorHandler` assumed that the errors passed to its
  `handleError()` method would be either strings or `Error` instances.
  _Apparently, other values (such as `null` or `undefined`) may also be
  passed._
- `window.onerror()` assumed that if an `Error` instance was passed in,
  it would always have a stacktrace (i.e. its `stack` property would be
  defined).
  _This is not necessarily true, although it is not clear (based on the
  logs) whether reported errors of this type are caused by `Error`
  instance with no stacktrace or by non-string error objects which are
  incorrectly treated as `Error` instances.

This commit ensures that all types of error arguments can be handled
correctly, including `Error` instances with no stacktrace and other
types of objects or primitives.

NOTE:
PR #42881 is related as it fixes handling `null` and `undefined`
arguments in the default `ErrorHandler`.

Fixes #28106

PR Close #42883

aio/src/app/shared/reporting-error-handler.spec.ts

@@ -56,10 +56,40 @@ describe('ReportingErrorHandler service', () => {
       expect(onerrorSpy).toHaveBeenCalledWith(error.message, undefined, undefined, undefined, error);
     });
 
+    it('should send a non-error object to window.onerror', () => {
+      const error = {reason: 'this is an error message'};
+      handler.handleError(error);
+      expect(onerrorSpy).toHaveBeenCalledWith(JSON.stringify(error));
+    });
+
+    it('should send a non-error object with circular references to window.onerror', () => {
+      const error = {
+        reason: 'this is an error message',
+        get self() { return this; },
+        toString() { return `{reason: ${this.reason}}`; },
+      };
+      handler.handleError(error);
+      expect(onerrorSpy).toHaveBeenCalledWith('{reason: this is an error message}');
+    });
+
     it('should send an error string to window.onerror', () => {
       const error = 'this is an error message';
       handler.handleError(error);
       expect(onerrorSpy).toHaveBeenCalledWith(error);
     });
+
+    it('should send a non-object, non-string error stringified to window.onerror', () => {
+      handler.handleError(404);
+      handler.handleError(false);
+      handler.handleError(null);
+      handler.handleError(undefined);
+
+      expect(onerrorSpy.calls.allArgs()).toEqual([
+        ['404'],
+        ['false'],
+        ['null'],
+        ['undefined'],
+      ]);
+    });
   });
 });

aio/src/app/shared/reporting-error-handler.ts

@@ -17,8 +17,7 @@ export class ReportingErrorHandler extends ErrorHandler {
    * Send error info to Google Analytics, in addition to the default handling.
    * @param error Information about the error.
    */
-  handleError(error: string | Error) {
-
+  handleError(error: any) {
     try {
       super.handleError(error);
     } catch (e) {
@@ -27,12 +26,19 @@ export class ReportingErrorHandler extends ErrorHandler {
     this.reportError(error);
   }
 
-  private reportError(error: string | Error) {
+  private reportError(error: unknown) {
     if (this.window.onerror) {
-      if (typeof error === 'string') {
-        this.window.onerror(error);
-      } else {
+      if (error instanceof Error) {
         this.window.onerror(error.message, undefined, undefined, undefined, error);
+      } else {
+        if (typeof error === 'object') {
+          try {
+            error = JSON.stringify(error);
+          } catch {
+            // Ignore the error and just let it be stringified.
+          }
+        }
+        this.window.onerror(`${error}`);
       }
     }
   }

aio/src/index.html

@@ -69,7 +69,7 @@
       function formatError(msg, url, line, col, e) {
         var stack;
         msg = msg.replace(/^Error: /, '');
-        if (e) {
+        if (e && e.stack) {
           stack = e.stack
             // strip the leading "Error: " from the stack trace
             .replace(/^Error: /, '')