diff --git a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
index 13bd13b804..0145b9f6e4 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
@@ -128,6 +128,7 @@ export class GrRepoCommands extends GestureEventListeners(
   }
 
   _handleRunningGC() {
+    if (!this.repo) return;
     this._runningGC = true;
     return this.restApiService
       .runRepoGC(this.repo)
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
index 085aa27f07..63019200f0 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
@@ -106,7 +106,7 @@ import {GrStorage, StorageLocation} from '../../shared/gr-storage/gr-storage';
 import {isAttentionSetEnabled} from '../../../utils/attention-set-util';
 import {CODE_REVIEW, getMaxAccounts} from '../../../utils/label-util';
 import {isUnresolved} from '../../../utils/comment-util';
-import {fireAlert} from '../../../utils/event-util';
+import {fireAlert, fireServerError} from '../../../utils/event-util';
 
 const STORAGE_DEBOUNCE_INTERVAL_MS = 400;
 
@@ -721,13 +721,7 @@ export class GrReplyDialog extends KeyboardShortcutMixin(
           return new Map<AccountId | EmailAddress, boolean>();
         }
         if (!response.ok) {
-          this.dispatchEvent(
-            new CustomEvent('server-error', {
-              detail: {response},
-              composed: true,
-              bubbles: true,
-            })
-          );
+          fireServerError(response);
           return new Map<AccountId | EmailAddress, boolean>();
         }
 
@@ -790,8 +784,9 @@ export class GrReplyDialog extends KeyboardShortcutMixin(
     return account._account_id === change.owner._account_id;
   }
 
-  _handle400Error(response?: Response | null) {
-    if (!response) throw new Error('Reponse is empty.');
+  _handle400Error(r?: Response | null) {
+    if (!r) throw new Error('Reponse is empty.');
+    let response: Response = r;
     // A call to _saveReview could fail with a server error if erroneous
     // reviewers were requested. This is signalled with a 400 Bad Request
     // status. The default gr-rest-api-interface error handling would
@@ -813,7 +808,7 @@ export class GrReplyDialog extends KeyboardShortcutMixin(
       const result = parsed as ReviewResult;
       // Only perform custom error handling for 400s and a parseable
       // ReviewResult response.
-      if (response && response.status === 400 && result && result.reviewers) {
+      if (response.status === 400 && result && result.reviewers) {
         const errors: string[] = [];
         const addReviewers = Object.values(result.reviewers);
         addReviewers.forEach(r => errors.push(r.error ?? 'no explanation'));
@@ -823,13 +818,7 @@ export class GrReplyDialog extends KeyboardShortcutMixin(
           text: () => Promise.resolve(errors.join(', ')),
         };
       }
-      this.dispatchEvent(
-        new CustomEvent('server-error', {
-          detail: {response},
-          composed: true,
-          bubbles: true,
-        })
-      );
+      fireServerError(response);
     });
   }
 
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
index a60662486b..3379cd4472 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
@@ -21,6 +21,7 @@ import './gr-reply-dialog.js';
 import {mockPromise} from '../../../test/test-utils.js';
 import {SpecialFilePath} from '../../../constants/constants.js';
 import {appContext} from '../../../services/app-context.js';
+import {addListenerForTest} from '../../../test/test-utils.js';
 
 const basicFixture = fixtureFromElement('gr-reply-dialog');
 
@@ -778,23 +779,23 @@ suite('gr-reply-dialog tests', () => {
     assert.isTrue(eraseDraftCommentStub.calledWith(location));
   });
 
-  test('400 converts to human-readable server-error', async () => {
+  test('400 converts to human-readable server-error', done => {
     sinon.stub(window, 'fetch').callsFake(() => {
       const text = '....{"reviewers":{"id1":{"error":"human readable"}}}';
       return Promise.resolve(cloneableResponse(400, text));
     });
 
-    let resolver;
-    const promise = new Promise(r => resolver = r);
-    element.addEventListener('server-error', resolver);
+    const listener = event => {
+      if (event.target !== document) return;
+      event.detail.response.text().then(body => {
+        if (body === 'human readable') {
+          done();
+        }
+      });
+    };
+    addListenerForTest(document, 'server-error', listener);
 
-    await flush();
-    element.send();
-
-    const event = await promise;
-    assert.equal(event.target, element);
-    const text = await event.detail.response.text();
-    assert.equal(text, 'human readable');
+    flush(() => { element.send(); });
   });
 
   test('non-json 400 is treated as a normal server-error', done => {
@@ -803,15 +804,15 @@ suite('gr-reply-dialog tests', () => {
       return Promise.resolve(cloneableResponse(400, text));
     });
 
-    element.addEventListener('server-error', event => {
-      if (event.target !== element) {
-        return;
-      }
+    const listener = event => {
+      if (event.target !== document) return;
       event.detail.response.text().then(body => {
-        assert.equal(body, 'Comment validation error!');
-        done();
+        if (body === 'Comment validation error!') {
+          done();
+        }
       });
-    });
+    };
+    addListenerForTest(document, 'server-error', listener);
 
     // Async tick is needed because iron-selector content is distributed and
     // distributed content requires an observer to be set up.
@@ -1255,12 +1256,13 @@ suite('gr-reply-dialog tests', () => {
         },
       },
     });
-    element.addEventListener('server-error', e => {
+    const listener = e => {
       e.detail.response.text().then(text => {
         assert.equal(text, [error1, error2, error3].join(', '));
         done();
       });
-    });
+    };
+    addListenerForTest(document, 'server-error', listener);
     element._handle400Error(cloneableResponse(400, text));
   });
 
diff --git a/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts b/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
index 4aa239a0a3..e868f03a40 100644
--- a/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
+++ b/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
@@ -34,10 +34,10 @@ import {EventEmitterService} from '../../../services/gr-event-interface/gr-event
 import {GrOverlay} from '../../shared/gr-overlay/gr-overlay';
 import {GrErrorDialog} from '../gr-error-dialog/gr-error-dialog';
 import {GrAlert} from '../../shared/gr-alert/gr-alert';
-import {FetchRequest} from '../../shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper';
 import {ErrorType, FixIronA11yAnnouncer} from '../../../types/types';
 import {AccountId} from '../../../types/common';
 import {EventType} from '../../../utils/event-util';
+import {NetworkErrorEvent, ServerErrorEvent} from '../../../types/events';
 
 const HIDE_ALERT_TIMEOUT_MS = 5000;
 const CHECK_SIGN_IN_INTERVAL_MS = 60 * 1000;
@@ -125,8 +125,8 @@ export class GrErrorManager extends GestureEventListeners(
   /** @override */
   attached() {
     super.attached();
-    this.listen(document, 'server-error', '_handleServerError');
-    this.listen(document, 'network-error', '_handleNetworkError');
+    this.listen(document, EventType.SERVER_ERROR, '_handleServerError');
+    this.listen(document, EventType.NETWORK_ERROR, '_handleNetworkError');
     this.listen(document, EventType.SHOW_ALERT, '_handleShowAlert');
     this.listen(document, 'hide-alert', '_hideAlert');
     this.listen(document, 'show-error', '_handleShowErrorDialog');
@@ -147,8 +147,8 @@ export class GrErrorManager extends GestureEventListeners(
   detached() {
     super.detached();
     this._clearHideAlertHandle();
-    this.unlisten(document, 'server-error', '_handleServerError');
-    this.unlisten(document, 'network-error', '_handleNetworkError');
+    this.unlisten(document, EventType.SERVER_ERROR, '_handleServerError');
+    this.unlisten(document, EventType.NETWORK_ERROR, '_handleNetworkError');
     this.unlisten(document, EventType.SHOW_ALERT, '_handleShowAlert');
     this.unlisten(document, 'hide-alert', '_hideAlert');
     this.unlisten(document, 'show-error', '_handleShowErrorDialog');
@@ -177,9 +177,7 @@ export class GrErrorManager extends GestureEventListeners(
     });
   }
 
-  _handleServerError(
-    e: CustomEvent<{response: Response; request: FetchRequest}>
-  ) {
+  _handleServerError(e: ServerErrorEvent) {
     const {request, response} = e.detail;
     response.text().then(errorText => {
       const url = request && (request.anonymizedUrl || request.url);
@@ -296,7 +294,7 @@ export class GrErrorManager extends GestureEventListeners(
     );
   }
 
-  _handleNetworkError(e: CustomEvent) {
+  _handleNetworkError(e: NetworkErrorEvent) {
     this._showAlert('Server unavailable');
     console.error(e.detail.error.message);
   }
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
index a267b0b427..3c401d018e 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
@@ -68,7 +68,11 @@ import {FilesWebLinks} from '../gr-patch-range-select/gr-patch-range-select';
 import {LineNumber, FILE} from '../gr-diff/gr-diff-line';
 import {GrCommentThread} from '../../shared/gr-comment-thread/gr-comment-thread';
 import {KnownExperimentId} from '../../../services/flags/flags';
-import {firePageError, fireAlert} from '../../../utils/event-util';
+import {
+  firePageError,
+  fireAlert,
+  fireServerError,
+} from '../../../utils/event-util';
 
 const MSG_EMPTY_BLAME = 'No blame information for this diff.';
 
@@ -591,13 +595,7 @@ export class GrDiffHost extends GestureEventListeners(
     // Loading the diff may respond with 409 if the file is too large. In this
     // case, use a toast error..
     if (response.status === 409) {
-      this.dispatchEvent(
-        new CustomEvent('server-error', {
-          detail: {response},
-          composed: true,
-          bubbles: true,
-        })
-      );
+      fireServerError(response);
       return;
     }
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
index 81a3604b40..9bde12243b 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
@@ -304,11 +304,15 @@ suite('gr-diff-host tests', () => {
 
       setup(() => {
         serverErrorStub = sinon.stub();
-        element.addEventListener('server-error', serverErrorStub);
+        document.addEventListener('server-error', serverErrorStub);
         pageErrorStub = sinon.stub();
         element.addEventListener('page-error', pageErrorStub);
       });
 
+      teardown(() => {
+        document.removeEventListener('server-error', serverErrorStub);
+      });
+
       test('page error on HTTP-409', () => {
         element._handleGetDiffError({status: 409});
         assert.isTrue(serverErrorStub.calledOnce);
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.ts b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.ts
index edb0113360..1c6e0b605f 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.ts
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.ts
@@ -157,7 +157,7 @@ import {
   HttpMethod,
   ReviewerState,
 } from '../../../constants/constants';
-import {firePageError} from '../../../utils/event-util';
+import {firePageError, fireServerError} from '../../../utils/event-util';
 
 const JSON_PREFIX = ")]}'";
 const MAX_PROJECT_RESULTS = 25;
@@ -408,19 +408,7 @@ export class GrRestApiInterface
     }) as Promise<DashboardInfo[] | undefined>;
   }
 
-  saveRepoConfig(repo: RepoName, config: ConfigInput): Promise<Response>;
-
-  saveRepoConfig(
-    repo: RepoName,
-    config: ConfigInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  saveRepoConfig(
-    repo: RepoName,
-    config: ConfigInput,
-    errFn?: ErrorCallback
-  ): Promise<Response | undefined> {
+  saveRepoConfig(repo: RepoName, config: ConfigInput): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const url = `/projects/${encodeURIComponent(repo)}/config`;
@@ -429,23 +417,11 @@ export class GrRestApiInterface
       method: HttpMethod.PUT,
       url,
       body: config,
-      errFn,
       anonymizedUrl: '/projects/*/config',
     });
   }
 
-  runRepoGC(repo: RepoName): Promise<Response>;
-
-  runRepoGC(
-    repo: RepoName,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  runRepoGC(repo: RepoName, errFn?: ErrorCallback) {
-    if (!repo) {
-      // TODO(TS): fix return value
-      return '';
-    }
+  runRepoGC(repo: RepoName): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(repo);
@@ -453,23 +429,11 @@ export class GrRestApiInterface
       method: HttpMethod.POST,
       url: `/projects/${encodeName}/gc`,
       body: '',
-      errFn,
       anonymizedUrl: '/projects/*/gc',
     });
   }
 
-  createRepo(config: ProjectInput & {name: RepoName}): Promise<Response>;
-
-  createRepo(
-    config: ProjectInput & {name: RepoName},
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  createRepo(config: ProjectInput, errFn?: ErrorCallback) {
-    if (!config.name) {
-      // TODO(TS): Fix return value
-      return '';
-    }
+  createRepo(config: ProjectInput & {name: RepoName}): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(config.name);
@@ -477,29 +441,16 @@ export class GrRestApiInterface
       method: HttpMethod.PUT,
       url: `/projects/${encodeName}`,
       body: config,
-      errFn,
       anonymizedUrl: '/projects/*',
     });
   }
 
-  createGroup(config: GroupInput & {name: string}): Promise<Response>;
-
-  createGroup(
-    config: GroupInput & {name: string},
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  createGroup(config: GroupInput, errFn?: ErrorCallback) {
-    if (!config.name) {
-      // TODO(TS): Fix return value
-      return '';
-    }
+  createGroup(config: GroupInput & {name: string}): Promise<Response> {
     const encodeName = encodeURIComponent(config.name);
     return this._restApiHelper.send({
       method: HttpMethod.PUT,
       url: `/groups/${encodeName}`,
       body: config,
-      errFn,
       anonymizedUrl: '/groups/*',
     });
   }
@@ -515,19 +466,7 @@ export class GrRestApiInterface
     }) as Promise<GroupInfo | undefined>;
   }
 
-  deleteRepoBranches(repo: RepoName, ref: GitRef): Promise<Response>;
-
-  deleteRepoBranches(
-    repo: RepoName,
-    ref: GitRef,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  deleteRepoBranches(repo: RepoName, ref: GitRef, errFn?: ErrorCallback) {
-    if (!repo || !ref) {
-      // TODO(TS): fix return value
-      return '';
-    }
+  deleteRepoBranches(repo: RepoName, ref: GitRef): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(repo);
@@ -536,24 +475,11 @@ export class GrRestApiInterface
       method: HttpMethod.DELETE,
       url: `/projects/${encodeName}/branches/${encodeRef}`,
       body: '',
-      errFn,
       anonymizedUrl: '/projects/*/branches/*',
     });
   }
 
-  deleteRepoTags(repo: RepoName, ref: GitRef): Promise<Response>;
-
-  deleteRepoTags(
-    repo: RepoName,
-    ref: GitRef,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  deleteRepoTags(repo: RepoName, ref: GitRef, errFn?: ErrorCallback) {
-    if (!repo || !ref) {
-      // TODO(TS): fix return type
-      return '';
-    }
+  deleteRepoTags(repo: RepoName, ref: GitRef): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(repo);
@@ -562,7 +488,6 @@ export class GrRestApiInterface
       method: HttpMethod.DELETE,
       url: `/projects/${encodeName}/tags/${encodeRef}`,
       body: '',
-      errFn,
       anonymizedUrl: '/projects/*/tags/*',
     });
   }
@@ -571,25 +496,7 @@ export class GrRestApiInterface
     name: RepoName,
     branch: BranchName,
     revision: BranchInput
-  ): Promise<Response>;
-
-  createRepoBranch(
-    name: RepoName,
-    branch: BranchName,
-    revision: BranchInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  createRepoBranch(
-    name: RepoName,
-    branch: BranchName,
-    revision: BranchInput,
-    errFn?: ErrorCallback
-  ) {
-    if (!name || !branch || !revision) {
-      // TODO(TS) fix return type
-      return '';
-    }
+  ): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(name);
@@ -598,7 +505,6 @@ export class GrRestApiInterface
       method: HttpMethod.PUT,
       url: `/projects/${encodeName}/branches/${encodeBranch}`,
       body: revision,
-      errFn,
       anonymizedUrl: '/projects/*/branches/*',
     });
   }
@@ -607,25 +513,7 @@ export class GrRestApiInterface
     name: RepoName,
     tag: string,
     revision: TagInput
-  ): Promise<Response>;
-
-  createRepoTag(
-    name: RepoName,
-    tag: string,
-    revision: TagInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  createRepoTag(
-    name: RepoName,
-    tag: string,
-    revision: TagInput,
-    errFn?: ErrorCallback
-  ) {
-    if (!name || !tag || !revision) {
-      // TODO(TS): Fix return value
-      return '';
-    }
+  ): Promise<Response> {
     // TODO(kaspern): Rename rest api from /projects/ to /repos/ once backend
     // supports it.
     const encodeName = encodeURIComponent(name);
@@ -634,7 +522,6 @@ export class GrRestApiInterface
       method: HttpMethod.PUT,
       url: `/projects/${encodeName}/tags/${encodeTag}`,
       body: revision,
-      errFn,
       anonymizedUrl: '/projects/*/tags/*',
     });
   }
@@ -650,16 +537,12 @@ export class GrRestApiInterface
     );
   }
 
-  getGroupMembers(
-    groupName: GroupId | GroupName,
-    errFn?: ErrorCallback
-  ): Promise<AccountInfo[] | undefined> {
+  getGroupMembers(groupName: GroupId | GroupName): Promise<AccountInfo[]> {
     const encodeName = encodeURIComponent(groupName);
-    return this._restApiHelper.fetchJSON({
+    return (this._restApiHelper.fetchJSON({
       url: `/groups/${encodeName}/members/`,
-      errFn,
       anonymizedUrl: '/groups/*/members',
-    }) as Promise<AccountInfo[] | undefined>;
+    }) as unknown) as Promise<AccountInfo[]>;
   }
 
   getIncludedGroup(
@@ -865,14 +748,7 @@ export class GrRestApiInterface
     });
   }
 
-  savePreferences(prefs: PreferencesInput): Promise<Response>;
-
-  savePreferences(
-    prefs: PreferencesInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  savePreferences(prefs: PreferencesInput, errFn?: ErrorCallback) {
+  savePreferences(prefs: PreferencesInput): Promise<Response> {
     // Note (Issue 5142): normalize the download scheme with lower case before
     // saving.
     if (prefs.download_scheme) {
@@ -883,45 +759,28 @@ export class GrRestApiInterface
       method: HttpMethod.PUT,
       url: '/accounts/self/preferences',
       body: prefs,
-      errFn,
       reportUrlAsIs: true,
     });
   }
 
-  saveDiffPreferences(prefs: DiffPreferenceInput): Promise<Response>;
-
-  saveDiffPreferences(
-    prefs: DiffPreferenceInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  saveDiffPreferences(prefs: DiffPreferenceInput, errFn?: ErrorCallback) {
+  saveDiffPreferences(prefs: DiffPreferenceInput): Promise<Response> {
     // Invalidate the cache.
     this._cache.delete('/accounts/self/preferences.diff');
     return this._restApiHelper.send({
       method: HttpMethod.PUT,
       url: '/accounts/self/preferences.diff',
       body: prefs,
-      errFn,
       reportUrlAsIs: true,
     });
   }
 
-  saveEditPreferences(prefs: EditPreferencesInfo): Promise<Response>;
-
-  saveEditPreferences(
-    prefs: EditPreferencesInfo,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
-  saveEditPreferences(prefs: EditPreferencesInfo, errFn?: ErrorCallback) {
+  saveEditPreferences(prefs: EditPreferencesInfo): Promise<Response> {
     // Invalidate the cache.
     this._cache.delete('/accounts/self/preferences.edit');
     return this._restApiHelper.send({
       method: HttpMethod.PUT,
       url: '/accounts/self/preferences.edit',
       body: prefs,
-      errFn,
       reportUrlAsIs: true,
     });
   }
@@ -1494,13 +1353,7 @@ export class GrRestApiInterface
             if (errFn) {
               errFn.call(null, response);
             } else {
-              document.dispatchEvent(
-                new CustomEvent('server-error', {
-                  detail: {request: req, response},
-                  composed: true,
-                  bubbles: true,
-                })
-              );
+              fireServerError(response, req);
             }
             return undefined;
           }
@@ -2207,14 +2060,8 @@ export class GrRestApiInterface
     // 404s indicate the file does not exist yet in the revision, so suppress
     // them.
     const suppress404s: ErrorCallback = res => {
-      if (res?.status !== 404) {
-        document.dispatchEvent(
-          new CustomEvent('server-error', {
-            detail: {res},
-            composed: true,
-            bubbles: true,
-          })
-        );
+      if (res && res?.status !== 404) {
+        fireServerError(res);
       }
       return res;
     };
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
index bd2818cb07..4bc7dd3c54 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
@@ -1294,7 +1294,7 @@ suite('gr-rest-api-interface tests', () => {
         })
         .then(() => {
           assert.isTrue(spy.called);
-          assert.notEqual(spy.lastCall.args[0].detail.res.status, 404);
+          assert.notEqual(spy.lastCall.args[0].detail.response.status, 404);
         });
   });
 
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
index 8aa1b0f13a..43a6af4d0a 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
@@ -32,6 +32,8 @@ import {
 } from '../../../../types/common';
 import {HttpMethod} from '../../../../constants/constants';
 import {RpcLogEventDetail} from '../../../../types/events';
+import {fireNetworkError, fireServerError} from '../../../../utils/event-util';
+import {FetchRequest} from '../../../../types/types';
 
 const JSON_PREFIX = ")]}'";
 
@@ -188,12 +190,6 @@ export interface SendJSONRequest extends SendRequestBase {
 
 export type SendRequest = SendRawRequest | SendJSONRequest;
 
-export interface FetchRequest {
-  url: string;
-  fetchOptions?: AuthRequestInit;
-  anonymizedUrl?: string;
-}
-
 export interface FetchJSONRequest extends FetchRequest {
   reportUrlAsIs?: boolean;
   params?: FetchParams;
@@ -315,13 +311,7 @@ s   */
         if (req.errFn) {
           req.errFn.call(undefined, null, err);
         } else {
-          document.dispatchEvent(
-            new CustomEvent('network-error', {
-              detail: {error: err},
-              composed: true,
-              bubbles: true,
-            })
-          );
+          fireNetworkError(err);
         }
         throw err;
       });
@@ -350,13 +340,7 @@ s   */
           req.errFn.call(null, response);
           return;
         }
-        document.dispatchEvent(
-          new CustomEvent('server-error', {
-            detail: {request: req, response},
-            composed: true,
-            bubbles: true,
-          })
-        );
+        fireServerError(response, req);
         return;
       }
       return this.getResponseObject(response);
@@ -510,13 +494,7 @@ s   */
     };
     const xhr = this.fetch(fetchReq)
       .catch(err => {
-        document.dispatchEvent(
-          new CustomEvent('network-error', {
-            detail: {error: err},
-            composed: true,
-            bubbles: true,
-          })
-        );
+        fireNetworkError(err);
         if (req.errFn) {
           return req.errFn.call(undefined, null, err);
         } else {
@@ -529,13 +507,7 @@ s   */
             req.errFn.call(undefined, response);
             return;
           }
-          document.dispatchEvent(
-            new CustomEvent('server-error', {
-              detail: {request: fetchReq, response},
-              composed: true,
-              bubbles: true,
-            })
-          );
+          fireServerError(response, fetchReq);
         }
         return response;
       });
diff --git a/polygerrit-ui/app/services/services/gr-rest-api/gr-rest-api.ts b/polygerrit-ui/app/services/services/gr-rest-api/gr-rest-api.ts
index cf064c1148..8a0f91279e 100644
--- a/polygerrit-ui/app/services/services/gr-rest-api/gr-rest-api.ts
+++ b/polygerrit-ui/app/services/services/gr-rest-api/gr-rest-api.ts
@@ -232,26 +232,10 @@ export interface RestApiService {
   getDiffPreferences(): Promise<DiffPreferencesInfo | undefined>;
 
   saveDiffPreferences(prefs: DiffPreferenceInput): Promise<Response>;
-  saveDiffPreferences(
-    prefs: DiffPreferenceInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-  saveDiffPreferences(
-    prefs: DiffPreferenceInput,
-    errFn?: ErrorCallback
-  ): Promise<Response>;
 
   getEditPreferences(): Promise<EditPreferencesInfo | undefined>;
 
   saveEditPreferences(prefs: EditPreferencesInfo): Promise<Response>;
-  saveEditPreferences(
-    prefs: EditPreferencesInfo,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-  saveEditPreferences(
-    prefs: EditPreferencesInfo,
-    errFn?: ErrorCallback
-  ): Promise<Response>;
 
   getAccountEmails(): Promise<EmailInfo[] | undefined>;
   deleteAccountEmail(email: string): Promise<Response>;
@@ -267,25 +251,11 @@ export interface RestApiService {
     revision: BranchInput
   ): Promise<Response>;
 
-  createRepoBranch(
-    name: RepoName,
-    branch: BranchName,
-    revision: BranchInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-
   createRepoTag(
     name: RepoName,
     tag: string,
     revision: TagInput
   ): Promise<Response>;
-
-  createRepoTag(
-    name: RepoName,
-    tag: string,
-    revision: TagInput,
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
   addAccountGPGKey(key: GpgKeysInput): Promise<Record<string, GpgKeyInfo>>;
   deleteAccountGPGKey(id: GpgKeyId): Promise<Response>;
   getAccountGPGKeys(): Promise<Record<string, GpgKeyInfo>>;
@@ -325,11 +295,6 @@ export interface RestApiService {
   ): Promise<ProjectAccessInfo | undefined>;
 
   createRepo(config: ProjectInput & {name: RepoName}): Promise<Response>;
-  createRepo(
-    config: ProjectInput & {name: RepoName},
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-  createRepo(config: ProjectInput, errFn?: ErrorCallback): Promise<Response>;
 
   getRepo(
     repo: RepoName,
@@ -522,11 +487,6 @@ export interface RestApiService {
     | Promise<PathToCommentsInfoMap | undefined>;
 
   createGroup(config: GroupInput & {name: string}): Promise<Response>;
-  createGroup(
-    config: GroupInput & {name: string},
-    errFn: ErrorCallback
-  ): Promise<Response | undefined>;
-  createGroup(config: GroupInput, errFn?: ErrorCallback): Promise<Response>;
 
   getPlugins(
     filter: string,
@@ -660,10 +620,7 @@ export interface RestApiService {
     errFn?: ErrorCallback
   ): Promise<GroupAuditEventInfo[] | undefined>;
 
-  getGroupMembers(
-    groupName: GroupId | GroupName,
-    errFn?: ErrorCallback
-  ): Promise<AccountInfo[] | undefined>;
+  getGroupMembers(groupName: GroupId | GroupName): Promise<AccountInfo[]>;
 
   getIncludedGroup(
     groupName: GroupId | GroupName
@@ -690,10 +647,7 @@ export interface RestApiService {
     includedGroup: GroupId
   ): Promise<Response>;
 
-  runRepoGC(
-    repo: RepoName,
-    errFn?: ErrorCallback
-  ): Promise<Response | undefined>;
+  runRepoGC(repo: RepoName): Promise<Response>;
   getFileContent(
     changeNum: NumericChangeId,
     path: string,
diff --git a/polygerrit-ui/app/test/test-utils.ts b/polygerrit-ui/app/test/test-utils.ts
index cccba5d5a9..08642af97e 100644
--- a/polygerrit-ui/app/test/test-utils.ts
+++ b/polygerrit-ui/app/test/test-utils.ts
@@ -105,6 +105,25 @@ export function registerTestCleanup(cleanupCallback: CleanupCallback) {
   cleanups.push(cleanupCallback);
 }
 
+export function addListenerForTest(
+  el: EventTarget,
+  type: string,
+  listener: EventListenerOrEventListenerObject
+) {
+  el.addEventListener(type, listener);
+  registerListenerCleanup(el, type, listener);
+}
+
+export function registerListenerCleanup(
+  el: EventTarget,
+  type: string,
+  listener: EventListenerOrEventListenerObject
+) {
+  registerTestCleanup(() => {
+    el.removeEventListener(type, listener);
+  });
+}
+
 export function cleanupTestUtils() {
   cleanups.forEach(cleanup => cleanup());
   cleanups.splice(0);
diff --git a/polygerrit-ui/app/types/events.ts b/polygerrit-ui/app/types/events.ts
index f136045669..e0b3348c5e 100644
--- a/polygerrit-ui/app/types/events.ts
+++ b/polygerrit-ui/app/types/events.ts
@@ -19,6 +19,7 @@ import {PatchSetNum} from './common';
 import {UIComment} from '../utils/comment-util';
 import {Side} from '../constants/constants';
 import {LineNumber} from '../elements/diff/gr-diff/gr-diff-line';
+import {FetchRequest} from './types';
 
 export interface TitleChangeEventDetail {
   title: string;
@@ -44,6 +45,31 @@ declare global {
   }
 }
 
+export interface ServerErrorEventDetail {
+  request?: FetchRequest;
+  response: Response;
+}
+
+export type ServerErrorEvent = CustomEvent<ServerErrorEventDetail>;
+
+declare global {
+  interface DocumentEventMap {
+    'server-error': ServerErrorEvent;
+  }
+}
+
+export interface NetworkErrorEventDetail {
+  error: Error;
+}
+
+export type NetworkErrorEvent = CustomEvent<NetworkErrorEventDetail>;
+
+declare global {
+  interface DocumentEventMap {
+    'network-error': NetworkErrorEvent;
+  }
+}
+
 export interface LocationChangeEventDetail {
   hash: string;
   pathname: string;
diff --git a/polygerrit-ui/app/types/types.ts b/polygerrit-ui/app/types/types.ts
index b40d618e47..232e204104 100644
--- a/polygerrit-ui/app/types/types.ts
+++ b/polygerrit-ui/app/types/types.ts
@@ -27,6 +27,7 @@ import {
   PatchSetNum,
 } from './common';
 import {PolymerSpliceChange} from '@polymer/polymer/interfaces';
+import {AuthRequestInit} from '../services/gr-auth/gr-auth';
 
 export function notUndefined<T>(x: T | undefined): x is T {
   return x !== undefined;
@@ -237,3 +238,9 @@ export function isPolymerSpliceChange<
 >(x: T | PolymerSpliceChange<U>): x is PolymerSpliceChange<U> {
   return (x as PolymerSpliceChange<U>).indexSplices !== undefined;
 }
+
+export interface FetchRequest {
+  url: string;
+  fetchOptions?: AuthRequestInit;
+  anonymizedUrl?: string;
+}
diff --git a/polygerrit-ui/app/utils/event-util.ts b/polygerrit-ui/app/utils/event-util.ts
index 0af8fe2b0c..36341bd493 100644
--- a/polygerrit-ui/app/utils/event-util.ts
+++ b/polygerrit-ui/app/utils/event-util.ts
@@ -15,9 +15,13 @@
  * limitations under the License.
  */
 
+import {FetchRequest} from '../types/types';
+
 export enum EventType {
   SHOW_ALERT = 'show-alert',
   PAGE_ERROR = 'page-error',
+  SERVER_ERROR = 'server-error',
+  NETWORK_ERROR = 'network-error',
   TITLE_CHANGE = 'title-change',
 }
 
@@ -41,6 +45,26 @@ export function firePageError(target: EventTarget, response?: Response | null) {
   );
 }
 
+export function fireServerError(response: Response, request?: FetchRequest) {
+  document.dispatchEvent(
+    new CustomEvent(EventType.SERVER_ERROR, {
+      detail: {response, request},
+      composed: true,
+      bubbles: true,
+    })
+  );
+}
+
+export function fireNetworkError(error: Error) {
+  document.dispatchEvent(
+    new CustomEvent(EventType.NETWORK_ERROR, {
+      detail: {error},
+      composed: true,
+      bubbles: true,
+    })
+  );
+}
+
 export function fireTitleChange(target: EventTarget, title: string) {
   target.dispatchEvent(
     new CustomEvent(EventType.TITLE_CHANGE, {