electron/lib/renderer/window-setup.ts

import { ipcRendererInternal } from '@electron/internal/renderer/ipc-renderer-internal';
import { internalContextBridge } from '@electron/internal/renderer/api/context-bridge';
import { IPC_MESSAGES } from '@electron/internal/common/ipc-messages';

const { contextIsolationEnabled } = internalContextBridge;

export const windowSetup = (isWebView: boolean, isHiddenPage: boolean) => {
  if (!process.sandboxed && !isWebView) {
    // Override default window.close.
    window.close = function () {
      ipcRendererInternal.send(IPC_MESSAGES.BROWSER_WINDOW_CLOSE);
    };
    if (contextIsolationEnabled) {
      internalContextBridge.overrideGlobalValueFromIsolatedWorld(['close'], window.close);
    }
  }

  // But we do not support prompt().
  window.prompt = function () {
    throw new Error('prompt() is and will not be supported.');
  };
  if (contextIsolationEnabled) {
    internalContextBridge.overrideGlobalValueFromIsolatedWorld(['prompt'], window.prompt);
  };

  if (isWebView) {
    // Webview `document.visibilityState` tracks visibility of the containing webContents.
    let cachedVisibilityState = isHiddenPage ? 'hidden' : 'visible';

    // Subscribe to visibilityState changes.
    ipcRendererInternal.on(IPC_MESSAGES.GUEST_INSTANCE_VISIBILITY_CHANGE, (_: Event, visibilityState: DocumentVisibilityState) => {
      if (cachedVisibilityState !== visibilityState) {
        cachedVisibilityState = visibilityState;
      }
    });

    // Make document.hidden and document.visibilityState return the correct value.
    const getDocumentHidden = () => cachedVisibilityState !== 'visible';
    Object.defineProperty(document, 'hidden', {
      get: getDocumentHidden
    });
    if (contextIsolationEnabled) {
      internalContextBridge.overrideGlobalPropertyFromIsolatedWorld(
        ['document', 'hidden'],
        getDocumentHidden
      );
    }

    const getDocumentVisibilityState = () => cachedVisibilityState;
    Object.defineProperty(document, 'visibilityState', {
      get: getDocumentVisibilityState
    });
    if (contextIsolationEnabled) {
      internalContextBridge.overrideGlobalPropertyFromIsolatedWorld(
        ['document', 'visibilityState'],
        getDocumentVisibilityState
      );
    }
  }
};