diff --git a/spec/api-app-spec.ts b/spec/api-app-spec.ts
index 0cade3e490..79c3388cb1 100644
--- a/spec/api-app-spec.ts
+++ b/spec/api-app-spec.ts
@@ -6,7 +6,7 @@ import * as net from 'node:net';
 import * as fs from 'fs-extra';
 import * as path from 'node:path';
 import { promisify } from 'node:util';
-import { app, BrowserWindow, Menu, session, net as electronNet } from 'electron/main';
+import { app, BrowserWindow, Menu, session, net as electronNet, WebContents } from 'electron/main';
 import { closeWindow, closeAllWindows } from './lib/window-helpers';
 import { ifdescribe, ifit, listen, waitUntil } from './lib/spec-helpers';
 import { once } from 'node:events';
@@ -495,7 +495,7 @@ describe('app module', () => {
     afterEach(() => closeWindow(w).then(() => { w = null as any; }));
 
     it('should emit browser-window-focus event when window is focused', async () => {
-      const emitted = once(app, 'browser-window-focus');
+      const emitted = once(app, 'browser-window-focus') as Promise<[any, BrowserWindow]>;
       w = new BrowserWindow({ show: false });
       w.emit('focus');
       const [, window] = await emitted;
@@ -503,7 +503,7 @@ describe('app module', () => {
     });
 
     it('should emit browser-window-blur event when window is blurred', async () => {
-      const emitted = once(app, 'browser-window-blur');
+      const emitted = once(app, 'browser-window-blur') as Promise<[any, BrowserWindow]>;
       w = new BrowserWindow({ show: false });
       w.emit('blur');
       const [, window] = await emitted;
@@ -511,14 +511,14 @@ describe('app module', () => {
     });
 
     it('should emit browser-window-created event when window is created', async () => {
-      const emitted = once(app, 'browser-window-created');
+      const emitted = once(app, 'browser-window-created') as Promise<[any, BrowserWindow]>;
       w = new BrowserWindow({ show: false });
       const [, window] = await emitted;
       expect(window.id).to.equal(w.id);
     });
 
     it('should emit web-contents-created event when a webContents is created', async () => {
-      const emitted = once(app, 'web-contents-created');
+      const emitted = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
       w = new BrowserWindow({ show: false });
       const [, webContents] = await emitted;
       expect(webContents.id).to.equal(w.webContents.id);
@@ -535,7 +535,7 @@ describe('app module', () => {
       });
       await w.loadURL('about:blank');
 
-      const emitted = once(app, 'renderer-process-crashed');
+      const emitted = once(app, 'renderer-process-crashed') as Promise<[any, WebContents]>;
       w.webContents.executeJavaScript('process.crash()');
 
       const [, webContents] = await emitted;
@@ -553,7 +553,7 @@ describe('app module', () => {
       });
       await w.loadURL('about:blank');
 
-      const emitted = once(app, 'render-process-gone');
+      const emitted = once(app, 'render-process-gone') as Promise<[any, WebContents, Electron.RenderProcessGoneDetails]>;
       w.webContents.executeJavaScript('process.crash()');
 
       const [, webContents, details] = await emitted;
@@ -1935,7 +1935,7 @@ describe('default behavior', () => {
     it('should emit a login event on app when a WebContents hits a 401', async () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL(serverUrl);
-      const [, webContents] = await once(app, 'login');
+      const [, webContents] = await once(app, 'login') as [any, WebContents];
       expect(webContents).to.equal(w.webContents);
     });
   });
diff --git a/spec/api-auto-updater-spec.ts b/spec/api-auto-updater-spec.ts
index 6c5ed269f1..ec0da4b9bd 100644
--- a/spec/api-auto-updater-spec.ts
+++ b/spec/api-auto-updater-spec.ts
@@ -6,7 +6,7 @@ import { once } from 'node:events';
 ifdescribe(!process.mas)('autoUpdater module', function () {
   describe('checkForUpdates', function () {
     ifit(process.platform === 'win32')('emits an error on Windows if the feed URL is not set', async function () {
-      const errorEvent = once(autoUpdater, 'error');
+      const errorEvent = once(autoUpdater, 'error') as Promise<[Error]>;
       autoUpdater.setFeedURL({ url: '' });
       autoUpdater.checkForUpdates();
       const [error] = await errorEvent;
@@ -56,7 +56,7 @@ ifdescribe(!process.mas)('autoUpdater module', function () {
 
     ifdescribe(process.platform === 'darwin' && process.arch !== 'arm64')('on Mac', function () {
       it('emits an error when the application is unsigned', async () => {
-        const errorEvent = once(autoUpdater, 'error');
+        const errorEvent = once(autoUpdater, 'error') as Promise<[Error]>;
         autoUpdater.setFeedURL({ url: '' });
         const [error] = await errorEvent;
         expect(error.message).equal('Could not get code signature for running application');
@@ -80,7 +80,7 @@ ifdescribe(!process.mas)('autoUpdater module', function () {
 
   describe('quitAndInstall', () => {
     ifit(process.platform === 'win32')('emits an error on Windows when no update is available', async function () {
-      const errorEvent = once(autoUpdater, 'error');
+      const errorEvent = once(autoUpdater, 'error') as Promise<[Error]>;
       autoUpdater.quitAndInstall();
       const [error] = await errorEvent;
       expect(error.message).to.equal('No update available, can\'t quit and install');
diff --git a/spec/api-browser-window-spec.ts b/spec/api-browser-window-spec.ts
index 9e1e7e7ec0..733d5e6272 100644
--- a/spec/api-browser-window-spec.ts
+++ b/spec/api-browser-window-spec.ts
@@ -2312,7 +2312,7 @@ describe('BrowserWindow module', () => {
     });
 
     it('causes the right value to be emitted on `always-on-top-changed`', async () => {
-      const alwaysOnTopChanged = once(w, 'always-on-top-changed');
+      const alwaysOnTopChanged = once(w, 'always-on-top-changed') as Promise<[any, boolean]>;
       expect(w.isAlwaysOnTop()).to.be.false('is alwaysOnTop');
       w.setAlwaysOnTop(true);
       const [, alwaysOnTop] = await alwaysOnTopChanged;
@@ -2694,7 +2694,7 @@ describe('BrowserWindow module', () => {
       // https://github.com/electron/electron/issues/25413, and is not integral
       // to the test.
       const p = once(w.webContents, 'did-attach-webview');
-      const [, webviewContents] = await once(app, 'web-contents-created');
+      const [, webviewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       expect(BrowserWindow.fromWebContents(webviewContents)!.id).to.equal(w.id);
       await p;
     });
@@ -3496,7 +3496,7 @@ describe('BrowserWindow module', () => {
         const pageUrl = 'file://' + htmlPath;
         const answer = once(ipcMain, 'answer');
         w.loadURL(pageUrl);
-        const [, { url, frameName, options }] = await once(w.webContents, 'did-create-window');
+        const [, { url, frameName, options }] = await once(w.webContents, 'did-create-window') as [BrowserWindow, Electron.DidCreateWindowDetails];
         const expectedUrl = process.platform === 'win32'
           ? 'file:///' + htmlPath.replace(/\\/g, '/')
           : pageUrl;
@@ -3542,7 +3542,7 @@ describe('BrowserWindow module', () => {
 
         // The page is going to open a popup that it won't be able to close.
         // We have to close it from here later.
-        const [, popupWindow] = await once(app, 'browser-window-created');
+        const [, popupWindow] = await once(app, 'browser-window-created') as [any, BrowserWindow];
 
         // Ask the popup window for details.
         const detailsAnswer = once(ipcMain, 'child-loaded');
@@ -3600,11 +3600,11 @@ describe('BrowserWindow module', () => {
         w.webContents.setWindowOpenHandler(() => ({ action: 'allow', overrideBrowserWindowOptions: { webPreferences: { preload: preloadPath, contextIsolation: false } } }));
         w.loadFile(path.join(fixtures, 'api', 'new-window.html'));
         const [[, childWebContents]] = await Promise.all([
-          once(app, 'web-contents-created'),
+          once(app, 'web-contents-created') as Promise<[any, WebContents]>,
           once(ipcMain, 'answer')
         ]);
         const webPreferences = childWebContents.getLastWebPreferences();
-        expect(webPreferences.contextIsolation).to.equal(false);
+        expect(webPreferences!.contextIsolation).to.equal(false);
       });
 
       it('should set ipc event sender correctly', async () => {
@@ -3736,7 +3736,7 @@ describe('BrowserWindow module', () => {
             contextIsolation: false
           }
         });
-        const didAttachWebview = once(w.webContents, 'did-attach-webview');
+        const didAttachWebview = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
         const webviewDomReady = once(ipcMain, 'webview-dom-ready');
         w.loadFile(path.join(fixtures, 'pages', 'webview-did-attach-event.html'));
 
@@ -3850,11 +3850,11 @@ describe('BrowserWindow module', () => {
         }));
         w.loadFile(path.join(fixtures, 'api', 'new-window.html'));
         const [[, childWebContents]] = await Promise.all([
-          once(app, 'web-contents-created'),
+          once(app, 'web-contents-created') as Promise<[any, WebContents]>,
           once(ipcMain, 'answer')
         ]);
         const webPreferences = childWebContents.getLastWebPreferences();
-        expect(webPreferences.contextIsolation).to.equal(false);
+        expect(webPreferences!.contextIsolation).to.equal(false);
       });
 
       describe('window.location', () => {
@@ -5952,10 +5952,10 @@ describe('BrowserWindow module', () => {
           preload: path.join(fixtures, 'api', 'isolated-preload.js')
         }
       });
-      const browserWindowCreated = once(app, 'browser-window-created');
+      const browserWindowCreated = once(app, 'browser-window-created') as Promise<[any, BrowserWindow]>;
       iw.loadFile(path.join(fixtures, 'pages', 'window-open.html'));
       const [, window] = await browserWindowCreated;
-      expect(window.webContents.getLastWebPreferences().contextIsolation).to.be.true('contextIsolation');
+      expect(window.webContents.getLastWebPreferences()!.contextIsolation).to.be.true('contextIsolation');
     });
     it('separates the page context from the Electron/preload context with sandbox on', async () => {
       const ws = new BrowserWindow({
@@ -6086,7 +6086,7 @@ describe('BrowserWindow module', () => {
     afterEach(closeAllWindows);
 
     it('creates offscreen window with correct size', async () => {
-      const paint = once(w.webContents, 'paint');
+      const paint = once(w.webContents, 'paint') as Promise<[any, Electron.Rectangle, Electron.NativeImage]>;
       w.loadFile(path.join(fixtures, 'api', 'offscreen-rendering.html'));
       const [,, data] = await paint;
       expect(data.constructor.name).to.equal('NativeImage');
@@ -6117,7 +6117,7 @@ describe('BrowserWindow module', () => {
 
     describe('window.webContents.isPainting()', () => {
       it('returns whether is currently painting', async () => {
-        const paint = once(w.webContents, 'paint');
+        const paint = once(w.webContents, 'paint') as Promise<[any, Electron.Rectangle, Electron.NativeImage]>;
         w.loadFile(path.join(fixtures, 'api', 'offscreen-rendering.html'));
         await paint;
         expect(w.webContents.isPainting()).to.be.true('isPainting');
@@ -6144,7 +6144,7 @@ describe('BrowserWindow module', () => {
         w.webContents.stopPainting();
         w.webContents.startPainting();
 
-        await once(w.webContents, 'paint');
+        await once(w.webContents, 'paint') as [any, Electron.Rectangle, Electron.NativeImage];
         expect(w.webContents.isPainting()).to.be.true('isPainting');
       });
     });
@@ -6152,13 +6152,13 @@ describe('BrowserWindow module', () => {
     describe('frameRate APIs', () => {
       it('has default frame rate (function)', async () => {
         w.loadFile(path.join(fixtures, 'api', 'offscreen-rendering.html'));
-        await once(w.webContents, 'paint');
+        await once(w.webContents, 'paint') as [any, Electron.Rectangle, Electron.NativeImage];
         expect(w.webContents.getFrameRate()).to.equal(60);
       });
 
       it('has default frame rate (property)', async () => {
         w.loadFile(path.join(fixtures, 'api', 'offscreen-rendering.html'));
-        await once(w.webContents, 'paint');
+        await once(w.webContents, 'paint') as [any, Electron.Rectangle, Electron.NativeImage];
         expect(w.webContents.frameRate).to.equal(60);
       });
 
@@ -6169,7 +6169,7 @@ describe('BrowserWindow module', () => {
 
         w.webContents.setFrameRate(30);
 
-        await once(w.webContents, 'paint');
+        await once(w.webContents, 'paint') as [any, Electron.Rectangle, Electron.NativeImage];
         expect(w.webContents.getFrameRate()).to.equal(30);
       });
 
@@ -6180,7 +6180,7 @@ describe('BrowserWindow module', () => {
 
         w.webContents.frameRate = 30;
 
-        await once(w.webContents, 'paint');
+        await once(w.webContents, 'paint') as [any, Electron.Rectangle, Electron.NativeImage];
         expect(w.webContents.frameRate).to.equal(30);
       });
     });
diff --git a/spec/api-native-theme-spec.ts b/spec/api-native-theme-spec.ts
index 8bba141ae2..524a905812 100644
--- a/spec/api-native-theme-spec.ts
+++ b/spec/api-native-theme-spec.ts
@@ -84,7 +84,7 @@ describe('nativeTheme module', () => {
           .addEventListener('change', () => require('electron').ipcRenderer.send('theme-change'))
       `);
       const originalSystemIsDark = await getPrefersColorSchemeIsDark(w);
-      let changePromise: Promise<any[]> = once(ipcMain, 'theme-change');
+      let changePromise = once(ipcMain, 'theme-change');
       nativeTheme.themeSource = 'dark';
       if (!originalSystemIsDark) await changePromise;
       expect(await getPrefersColorSchemeIsDark(w)).to.equal(true);
diff --git a/spec/api-session-spec.ts b/spec/api-session-spec.ts
index 7d483e6f9b..7dc9930b51 100644
--- a/spec/api-session-spec.ts
+++ b/spec/api-session-spec.ts
@@ -1412,7 +1412,7 @@ describe('session module', () => {
 
   describe('session-created event', () => {
     it('is emitted when a session is created', async () => {
-      const sessionCreated = once(app, 'session-created');
+      const sessionCreated = once(app, 'session-created') as Promise<[any, Session]>;
       const session1 = session.fromPartition('' + Math.random());
       const [session2] = await sessionCreated;
       expect(session1).to.equal(session2);
diff --git a/spec/api-web-contents-spec.ts b/spec/api-web-contents-spec.ts
index 63af200d5d..7445111b63 100644
--- a/spec/api-web-contents-spec.ts
+++ b/spec/api-web-contents-spec.ts
@@ -3,7 +3,7 @@ import { AddressInfo } from 'node:net';
 import * as path from 'node:path';
 import * as fs from 'node:fs';
 import * as http from 'node:http';
-import { BrowserWindow, ipcMain, webContents, session, app, BrowserView } from 'electron/main';
+import { BrowserWindow, ipcMain, webContents, session, app, BrowserView, WebContents } from 'electron/main';
 import { closeAllWindows } from './lib/window-helpers';
 import { ifdescribe, defer, waitUntil, listen, ifit } from './lib/spec-helpers';
 import { once } from 'node:events';
@@ -24,7 +24,7 @@ describe('webContents module', () => {
       });
       w.loadFile(path.join(fixturesPath, 'pages', 'webview-zoom-factor.html'));
 
-      await once(w.webContents, 'did-attach-webview');
+      await once(w.webContents, 'did-attach-webview') as [any, WebContents];
 
       w.webContents.openDevTools();
 
@@ -637,7 +637,7 @@ describe('webContents module', () => {
         if (opts.meta) modifiers.push('meta');
         if (opts.isAutoRepeat) modifiers.push('isAutoRepeat');
 
-        const p = once(w.webContents, 'before-input-event');
+        const p = once(w.webContents, 'before-input-event') as Promise<[any, Electron.Input]>;
         w.webContents.sendInputEvent({
           type: opts.type,
           keyCode: opts.keyCode,
@@ -720,7 +720,7 @@ describe('webContents module', () => {
           modifiers: ['control', 'meta']
         });
 
-        const [, zoomDirection] = await once(w.webContents, 'zoom-changed');
+        const [, zoomDirection] = await once(w.webContents, 'zoom-changed') as [any, string];
         expect(zoomDirection).to.equal('in');
       };
 
@@ -743,7 +743,7 @@ describe('webContents module', () => {
           modifiers: ['control', 'meta']
         });
 
-        const [, zoomDirection] = await once(w.webContents, 'zoom-changed');
+        const [, zoomDirection] = await once(w.webContents, 'zoom-changed') as [any, string];
         expect(zoomDirection).to.equal('out');
       };
 
@@ -1293,7 +1293,7 @@ describe('webContents module', () => {
     it('can get opener with window.open()', async () => {
       const w = new BrowserWindow({ show: false, webPreferences: { sandbox: true } });
       await w.loadURL('about:blank');
-      const childPromise = once(w.webContents, 'did-create-window');
+      const childPromise = once(w.webContents, 'did-create-window') as Promise<[BrowserWindow, Electron.DidCreateWindowDetails]>;
       w.webContents.executeJavaScript('window.open("about:blank")', true);
       const [childWindow] = await childPromise;
       expect(childWindow.webContents.opener).to.equal(w.webContents.mainFrame);
@@ -1301,7 +1301,7 @@ describe('webContents module', () => {
     it('has no opener when using "noopener"', async () => {
       const w = new BrowserWindow({ show: false, webPreferences: { sandbox: true } });
       await w.loadURL('about:blank');
-      const childPromise = once(w.webContents, 'did-create-window');
+      const childPromise = once(w.webContents, 'did-create-window') as Promise<[BrowserWindow, Electron.DidCreateWindowDetails]>;
       w.webContents.executeJavaScript('window.open("about:blank", undefined, "noopener")', true);
       const [childWindow] = await childPromise;
       expect(childWindow.webContents.opener).to.be.null();
@@ -1309,7 +1309,7 @@ describe('webContents module', () => {
     it('can get opener with a[target=_blank][rel=opener]', async () => {
       const w = new BrowserWindow({ show: false, webPreferences: { sandbox: true } });
       await w.loadURL('about:blank');
-      const childPromise = once(w.webContents, 'did-create-window');
+      const childPromise = once(w.webContents, 'did-create-window') as Promise<[BrowserWindow, Electron.DidCreateWindowDetails]>;
       w.webContents.executeJavaScript(`(function() {
         const a = document.createElement('a');
         a.target = '_blank';
@@ -1323,7 +1323,7 @@ describe('webContents module', () => {
     it('has no opener with a[target=_blank][rel=noopener]', async () => {
       const w = new BrowserWindow({ show: false, webPreferences: { sandbox: true } });
       await w.loadURL('about:blank');
-      const childPromise = once(w.webContents, 'did-create-window');
+      const childPromise = once(w.webContents, 'did-create-window') as Promise<[BrowserWindow, Electron.DidCreateWindowDetails]>;
       w.webContents.executeJavaScript(`(function() {
         const a = document.createElement('a');
         a.target = '_blank';
@@ -1485,7 +1485,7 @@ describe('webContents module', () => {
 
       it('forcefullyCrashRenderer() crashes the process with reason=killed||crashed', async () => {
         expect(w.webContents.isCrashed()).to.equal(false);
-        const crashEvent = once(w.webContents, 'render-process-gone');
+        const crashEvent = once(w.webContents, 'render-process-gone') as Promise<[any, Electron.RenderProcessGoneDetails]>;
         w.webContents.forcefullyCrashRenderer();
         const [, details] = await crashEvent;
         expect(details.reason === 'killed' || details.reason === 'crashed').to.equal(true, 'reason should be killed || crashed');
@@ -1716,7 +1716,7 @@ describe('webContents module', () => {
             }
           });
 
-          const promise = once(w.webContents, 'preload-error');
+          const promise = once(w.webContents, 'preload-error') as Promise<[any, string, Error]>;
           w.loadURL('about:blank');
 
           const [, preloadPath, error] = await promise;
@@ -1735,7 +1735,7 @@ describe('webContents module', () => {
             }
           });
 
-          const promise = once(w.webContents, 'preload-error');
+          const promise = once(w.webContents, 'preload-error') as Promise<[any, string, Error]>;
           w.loadURL('about:blank');
 
           const [, preloadPath, error] = await promise;
@@ -1754,7 +1754,7 @@ describe('webContents module', () => {
             }
           });
 
-          const promise = once(w.webContents, 'preload-error');
+          const promise = once(w.webContents, 'preload-error') as Promise<[any, string, Error]>;
           w.loadURL('about:blank');
 
           const [, preloadPath, error] = await promise;
@@ -2227,9 +2227,9 @@ describe('webContents module', () => {
       const bw = new BrowserWindow({ show: false });
       await bw.loadURL('about:blank');
       bw.webContents.executeJavaScript('child = window.open("", "", "show=no"); null');
-      const [, child] = await once(app, 'web-contents-created');
+      const [, child] = await once(app, 'web-contents-created') as [any, WebContents];
       bw.webContents.executeJavaScript('child.document.title = "new title"');
-      const [, title] = await once(child, 'page-title-updated');
+      const [, title] = await once(child, 'page-title-updated') as [any, string];
       expect(title).to.equal('new title');
     });
   });
@@ -2251,7 +2251,7 @@ describe('webContents module', () => {
       const w = new BrowserWindow({ show: false });
       await w.loadFile(path.join(fixturesPath, 'pages', 'base-page.html'));
 
-      const promise = once(w.webContents, 'context-menu');
+      const promise = once(w.webContents, 'context-menu') as Promise<[any, Electron.ContextMenuParams]>;
 
       // Simulate right-click to create context-menu event.
       const opts = { x: 0, y: 0, button: 'right' as any };
@@ -2350,7 +2350,7 @@ describe('webContents module', () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL('about:blank');
       w.webContents.executeJavaScript('window.moveTo(100, 100)', true);
-      const [, rect] = await once(w.webContents, 'content-bounds-updated');
+      const [, rect] = await once(w.webContents, 'content-bounds-updated') as [any, Electron.Rectangle];
       const { width, height } = w.getBounds();
       expect(rect).to.deep.equal({
         x: 100,
@@ -2367,7 +2367,7 @@ describe('webContents module', () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL('about:blank');
       w.webContents.executeJavaScript('window.resizeTo(100, 100)', true);
-      const [, rect] = await once(w.webContents, 'content-bounds-updated');
+      const [, rect] = await once(w.webContents, 'content-bounds-updated') as [any, Electron.Rectangle];
       const { x, y } = w.getBounds();
       expect(rect).to.deep.equal({
         x,
diff --git a/spec/api-web-frame-main-spec.ts b/spec/api-web-frame-main-spec.ts
index 2da465a130..2acf53528d 100644
--- a/spec/api-web-frame-main-spec.ts
+++ b/spec/api-web-frame-main-spec.ts
@@ -143,7 +143,7 @@ describe('webFrameMain module', () => {
     it('should show parent origin when child page is about:blank', async () => {
       const w = new BrowserWindow({ show: false });
       await w.loadFile(path.join(fixtures, 'pages', 'blank.html'));
-      const webContentsCreated: Promise<[unknown, WebContents]> = once(app, 'web-contents-created') as any;
+      const webContentsCreated = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
       expect(w.webContents.mainFrame.origin).to.equal('file://');
       await w.webContents.executeJavaScript('window.open("", null, "show=false"), null');
       const [, childWebContents] = await webContentsCreated;
@@ -163,7 +163,7 @@ describe('webFrameMain module', () => {
       expect(mainFrame.origin).to.equal(serverA.url.replace(/\/$/, ''));
       const [childFrame] = mainFrame.frames;
       expect(childFrame.origin).to.equal(serverB.url.replace(/\/$/, ''));
-      const webContentsCreated: Promise<[unknown, WebContents]> = once(app, 'web-contents-created') as any;
+      const webContentsCreated = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
       await childFrame.executeJavaScript('window.open("", null, "show=false"), null');
       const [, childWebContents] = await webContentsCreated;
       expect(childWebContents.mainFrame.origin).to.equal(childFrame.origin);
@@ -367,7 +367,7 @@ describe('webFrameMain module', () => {
   describe('"frame-created" event', () => {
     it('emits when the main frame is created', async () => {
       const w = new BrowserWindow({ show: false });
-      const promise = once(w.webContents, 'frame-created');
+      const promise = once(w.webContents, 'frame-created') as Promise<[any, Electron.FrameCreatedDetails]>;
       w.webContents.loadFile(path.join(subframesPath, 'frame.html'));
       const [, details] = await promise;
       expect(details.frame).to.equal(w.webContents.mainFrame);
@@ -375,7 +375,7 @@ describe('webFrameMain module', () => {
 
     it('emits when nested frames are created', async () => {
       const w = new BrowserWindow({ show: false });
-      const promise = emittedNTimes(w.webContents, 'frame-created', 2);
+      const promise = emittedNTimes(w.webContents, 'frame-created', 2) as Promise<[any, Electron.FrameCreatedDetails][]>;
       w.webContents.loadFile(path.join(subframesPath, 'frame-container.html'));
       const [[, mainDetails], [, nestedDetails]] = await promise;
       expect(mainDetails.frame).to.equal(w.webContents.mainFrame);
diff --git a/spec/chromium-spec.ts b/spec/chromium-spec.ts
index 99735ef204..06fd360ab5 100644
--- a/spec/chromium-spec.ts
+++ b/spec/chromium-spec.ts
@@ -107,7 +107,7 @@ describe('focus handling', () => {
       }
     });
 
-    const webviewReady = once(w.webContents, 'did-attach-webview');
+    const webviewReady = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
     await w.loadFile(path.join(fixturesPath, 'pages', 'tab-focus-loop-elements.html'));
     const [, wvContents] = await webviewReady;
     webviewContents = wvContents;
@@ -940,7 +940,7 @@ describe('chromium features', () => {
 
           await w.loadFile(path.join(fixturesPath, 'pages', 'form-with-data.html'));
 
-          const windowCreatedPromise = once(app, 'browser-window-created');
+          const windowCreatedPromise = once(app, 'browser-window-created') as Promise<[any, BrowserWindow]>;
 
           w.webContents.executeJavaScript(`
             const form = document.querySelector('form')
@@ -972,7 +972,7 @@ describe('chromium features', () => {
 
         defer(() => { w.close(); });
 
-        const promise = once(app, 'browser-window-created');
+        const promise = once(app, 'browser-window-created') as Promise<[any, BrowserWindow]>;
         w.loadFile(path.join(fixturesPath, 'pages', 'window-open.html'));
         const [, newWindow] = await promise;
         expect(newWindow.isVisible()).to.equal(true);
@@ -1008,7 +1008,7 @@ describe('chromium features', () => {
       w.webContents.executeJavaScript(`
         { b = window.open('devtools://devtools/bundled/inspector.html', '', 'nodeIntegration=no,show=no'); null }
       `);
-      const [, contents] = await once(app, 'web-contents-created');
+      const [, contents] = await once(app, 'web-contents-created') as [any, WebContents];
       const typeofProcessGlobal = await contents.executeJavaScript('typeof process');
       expect(typeofProcessGlobal).to.equal('undefined');
     });
@@ -1019,7 +1019,7 @@ describe('chromium features', () => {
       w.webContents.executeJavaScript(`
         { b = window.open('about:blank', '', 'nodeIntegration=no,show=no'); null }
       `);
-      const [, contents] = await once(app, 'web-contents-created');
+      const [, contents] = await once(app, 'web-contents-created') as [any, WebContents];
       const typeofProcessGlobal = await contents.executeJavaScript('typeof process');
       expect(typeofProcessGlobal).to.equal('undefined');
     });
@@ -1036,14 +1036,14 @@ describe('chromium features', () => {
       w.webContents.executeJavaScript(`
         { b = window.open(${JSON.stringify(windowUrl)}, '', 'javascript=no,show=no'); null }
       `);
-      const [, contents] = await once(app, 'web-contents-created');
+      const [, contents] = await once(app, 'web-contents-created') as [any, WebContents];
       await once(contents, 'did-finish-load');
       // Click link on page
       contents.sendInputEvent({ type: 'mouseDown', clickCount: 1, x: 1, y: 1 });
       contents.sendInputEvent({ type: 'mouseUp', clickCount: 1, x: 1, y: 1 });
-      const [, window] = await once(app, 'browser-window-created');
+      const [, window] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       const preferences = window.webContents.getLastWebPreferences();
-      expect(preferences.javascript).to.be.false();
+      expect(preferences!.javascript).to.be.false();
     });
 
     it('defines a window.location getter', async () => {
@@ -1056,7 +1056,7 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       w.webContents.loadFile(path.resolve(__dirname, 'fixtures', 'blank.html'));
       w.webContents.executeJavaScript(`{ b = window.open(${JSON.stringify(targetURL)}); null }`);
-      const [, window] = await once(app, 'browser-window-created');
+      const [, window] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       await once(window.webContents, 'did-finish-load');
       expect(await w.webContents.executeJavaScript('b.location.href')).to.equal(targetURL);
     });
@@ -1065,7 +1065,7 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       w.webContents.loadFile(path.resolve(__dirname, 'fixtures', 'blank.html'));
       w.webContents.executeJavaScript('{ b = window.open("about:blank"); null }');
-      const [, { webContents }] = await once(app, 'browser-window-created');
+      const [, { webContents }] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       await once(webContents, 'did-finish-load');
       // When it loads, redirect
       w.webContents.executeJavaScript(`{ b.location = ${JSON.stringify(`file://${fixturesPath}/pages/base-page.html`)}; null }`);
@@ -1076,7 +1076,7 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       w.webContents.loadFile(path.resolve(__dirname, 'fixtures', 'blank.html'));
       w.webContents.executeJavaScript('{ b = window.open("about:blank"); null }');
-      const [, { webContents }] = await once(app, 'browser-window-created');
+      const [, { webContents }] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       await once(webContents, 'did-finish-load');
       // When it loads, redirect
       w.webContents.executeJavaScript(`{ b.location.href = ${JSON.stringify(`file://${fixturesPath}/pages/base-page.html`)}; null }`);
@@ -1087,7 +1087,7 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL('about:blank');
       w.webContents.executeJavaScript('{ b = window.open(); null }');
-      const [, { webContents }] = await once(app, 'browser-window-created');
+      const [, { webContents }] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       await once(webContents, 'did-finish-load');
       expect(await w.webContents.executeJavaScript('b.location.href')).to.equal('about:blank');
     });
@@ -1096,7 +1096,7 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL('about:blank');
       w.webContents.executeJavaScript('{ b = window.open(\'\'); null }');
-      const [, { webContents }] = await once(app, 'browser-window-created');
+      const [, { webContents }] = await once(app, 'browser-window-created') as [any, BrowserWindow];
       await once(webContents, 'did-finish-load');
       expect(await w.webContents.executeJavaScript('b.location.href')).to.equal('about:blank');
     });
@@ -1864,7 +1864,7 @@ describe('chromium features', () => {
     it('opens when loading a pdf resource as top level navigation', async () => {
       const w = new BrowserWindow({ show: false });
       w.loadURL(pdfSource);
-      const [, contents] = await once(app, 'web-contents-created');
+      const [, contents] = await once(app, 'web-contents-created') as [any, WebContents];
       await once(contents, 'did-navigate');
       expect(contents.getURL()).to.equal('chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai/index.html');
     });
@@ -1872,7 +1872,7 @@ describe('chromium features', () => {
     it('opens when loading a pdf resource in a iframe', async () => {
       const w = new BrowserWindow({ show: false });
       w.loadFile(path.join(__dirname, 'fixtures', 'pages', 'pdf-in-iframe.html'));
-      const [, contents] = await once(app, 'web-contents-created');
+      const [, contents] = await once(app, 'web-contents-created') as [any, WebContents];
       await once(contents, 'did-navigate');
       expect(contents.getURL()).to.equal('chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai/index.html');
     });
diff --git a/spec/extensions-spec.ts b/spec/extensions-spec.ts
index b0cc0f6e63..5e04888249 100644
--- a/spec/extensions-spec.ts
+++ b/spec/extensions-spec.ts
@@ -54,7 +54,7 @@ describe('chrome extensions', () => {
     const w = new BrowserWindow({ show: false, webPreferences: { session: customSession, sandbox: true } });
     await w.loadURL('about:blank');
 
-    const promise = once(app, 'web-contents-created');
+    const promise = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
     await customSession.loadExtension(path.join(fixtures, 'extensions', 'persistent-background-page'));
     const args: any = await promise;
     const wc: Electron.WebContents = args[1];
@@ -74,7 +74,7 @@ describe('chrome extensions', () => {
     const w = new BrowserWindow({ show: false, webPreferences: { session: customSession, sandbox: true } });
     await w.loadURL('about:blank');
 
-    const promise = once(app, 'web-contents-created');
+    const promise = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
     await customSession.loadExtension(path.join(fixtures, 'extensions', 'persistent-background-page'));
     const args: any = await promise;
     const wc: Electron.WebContents = args[1];
@@ -457,7 +457,7 @@ describe('chrome extensions', () => {
 
     it('has session in background page', async () => {
       const customSession = session.fromPartition(`persist:${require('uuid').v4()}`);
-      const promise = once(app, 'web-contents-created');
+      const promise = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
       const { id } = await customSession.loadExtension(path.join(fixtures, 'extensions', 'persistent-background-page'));
       const [, bgPageContents] = await promise;
       expect(bgPageContents.getType()).to.equal('backgroundPage');
@@ -468,7 +468,7 @@ describe('chrome extensions', () => {
 
     it('can open devtools of background page', async () => {
       const customSession = session.fromPartition(`persist:${require('uuid').v4()}`);
-      const promise = once(app, 'web-contents-created');
+      const promise = once(app, 'web-contents-created') as Promise<[any, WebContents]>;
       await customSession.loadExtension(path.join(fixtures, 'extensions', 'persistent-background-page'));
       const [, bgPageContents] = await promise;
       expect(bgPageContents.getType()).to.equal('backgroundPage');
diff --git a/spec/guest-window-manager-spec.ts b/spec/guest-window-manager-spec.ts
index 7a964964dd..621de49122 100644
--- a/spec/guest-window-manager-spec.ts
+++ b/spec/guest-window-manager-spec.ts
@@ -182,7 +182,7 @@ describe('webContents.setWindowOpenHandler', () => {
   it('can change webPreferences of child windows', async () => {
     browserWindow.webContents.setWindowOpenHandler(() => ({ action: 'allow', overrideBrowserWindowOptions: { webPreferences: { defaultFontSize: 30 } } }));
 
-    const didCreateWindow = once(browserWindow.webContents, 'did-create-window');
+    const didCreateWindow = once(browserWindow.webContents, 'did-create-window') as Promise<[BrowserWindow, Electron.DidCreateWindowDetails]>;
     browserWindow.webContents.executeJavaScript("window.open('about:blank', '', 'show=no') && true");
     const [childWindow] = await didCreateWindow;
 
diff --git a/spec/webview-spec.ts b/spec/webview-spec.ts
index 8213058f32..51c2ab952b 100644
--- a/spec/webview-spec.ts
+++ b/spec/webview-spec.ts
@@ -208,7 +208,7 @@ describe('<webview> tag', function () {
           contextIsolation: false
         }
       });
-      const didAttachWebview = once(w.webContents, 'did-attach-webview');
+      const didAttachWebview = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
       const webviewDomReady = once(ipcMain, 'webview-dom-ready');
       w.loadFile(path.join(fixtures, 'pages', 'webview-did-attach-event.html'));
 
@@ -434,7 +434,7 @@ describe('<webview> tag', function () {
           contextIsolation: false
         }
       });
-      const attachPromise = once(w.webContents, 'did-attach-webview');
+      const attachPromise = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
       const readyPromise = once(ipcMain, 'dom-ready');
       w.loadFile(path.join(fixtures, 'pages', 'webview-zoom-inherited.html'));
       const [, webview] = await attachPromise;
@@ -453,7 +453,7 @@ describe('<webview> tag', function () {
           contextIsolation: false
         }
       });
-      const attachPromise = once(w.webContents, 'did-attach-webview');
+      const attachPromise = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
       await w.loadFile(path.join(fixtures, 'pages', 'webview-zoom-inherited.html'));
       await attachPromise;
       await w.webContents.executeJavaScript('view.remove()');
@@ -463,7 +463,7 @@ describe('<webview> tag', function () {
 
   describe('requestFullscreen from webview', () => {
     afterEach(closeAllWindows);
-    const loadWebViewWindow = async () => {
+    async function loadWebViewWindow (): Promise<[BrowserWindow, WebContents]> {
       const w = new BrowserWindow({
         webPreferences: {
           webviewTag: true,
@@ -472,7 +472,7 @@ describe('<webview> tag', function () {
         }
       });
 
-      const attachPromise = once(w.webContents, 'did-attach-webview');
+      const attachPromise = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
       const loadPromise = once(w.webContents, 'did-finish-load');
       const readyPromise = once(ipcMain, 'webview-ready');
 
@@ -572,7 +572,7 @@ describe('<webview> tag', function () {
         }
       });
 
-      const didAttachWebview = once(w.webContents, 'did-attach-webview');
+      const didAttachWebview = once(w.webContents, 'did-attach-webview') as Promise<[any, WebContents]>;
       w.loadFile(path.join(fixtures, 'pages', 'webview-did-attach-event.html'));
 
       const [, webContents] = await didAttachWebview;
@@ -792,7 +792,7 @@ describe('<webview> tag', function () {
         partition,
         nodeintegration: 'on'
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       setUpRequestHandler(webViewContents.id, 'media');
       const [, errorName] = await errorFromRenderer;
       expect(errorName).to.equal('PermissionDeniedError');
@@ -806,7 +806,7 @@ describe('<webview> tag', function () {
         nodeintegration: 'on',
         webpreferences: 'contextIsolation=no'
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       setUpRequestHandler(webViewContents.id, 'geolocation');
       const [, error] = await errorFromRenderer;
       expect(error).to.equal('User denied Geolocation');
@@ -820,7 +820,7 @@ describe('<webview> tag', function () {
         nodeintegration: 'on',
         webpreferences: 'contextIsolation=no'
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       setUpRequestHandler(webViewContents.id, 'midi');
       const [, error] = await errorFromRenderer;
       expect(error).to.equal('SecurityError');
@@ -834,7 +834,7 @@ describe('<webview> tag', function () {
         nodeintegration: 'on',
         webpreferences: 'contextIsolation=no'
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       setUpRequestHandler(webViewContents.id, 'midiSysex');
       const [, error] = await errorFromRenderer;
       expect(error).to.equal('SecurityError');
@@ -845,7 +845,7 @@ describe('<webview> tag', function () {
         src: 'magnet:test',
         partition
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
       await setUpRequestHandler(webViewContents.id, 'openExternal');
     });
 
@@ -857,7 +857,7 @@ describe('<webview> tag', function () {
         nodeintegration: 'on',
         webpreferences: 'contextIsolation=no'
       });
-      const [, webViewContents] = await once(app, 'web-contents-created');
+      const [, webViewContents] = await once(app, 'web-contents-created') as [any, WebContents];
 
       await setUpRequestHandler(webViewContents.id, 'notifications');