fix: spy on popup apis like alert (#3076)

Co-authored-by: Vladimir <sleuths.slews0s@icloud.com>

docs/guide/browser.md

@@ -1,8 +1,8 @@
 ---
-title: Browser mode | Guide
+title: Browser Mode | Guide
 ---
 
-# Browser mode (experimental)
+# Browser Mode (experimental)
 
 This page provides information about the experimental browser mode feature in the Vitest API, which allows you to run your tests in the browser natively, providing access to browser globals like window and document. This feature is currently under development, and APIs may change in the future.
 
@@ -87,3 +87,10 @@ npx vitest --browser.name=chrome --browser.headless
 ```
 
 In this case, Vitest will run in headless mode using the Chrome browser.
+
+## Limitations
+### Thread Blocking Dialogs
+
+When using Vitest Browser, it's important to note that thread blocking dialogs like `alert` or `confirm` cannot be used natively. This is because they block the web page, which means Vitest cannot continue communicating with the page, causing the execution to hang.
+
+In such situations, Vitest provides default mocks with default returned values for these APIs. This ensures that if the user accidentally uses synchronous popup web APIs, the execution would not hang. However, it's still recommended for the user to mock these web APIs for better experience. Read more in [Mocking](/guide/mocking).

packages/browser/src/client/dialog.ts

@@ -0,0 +1,21 @@
+const showPopupWarning = <T>(name: string, value: T, defaultValue?: T) => (...params: any[]) => {
+  const formatedParams = params.map(p => JSON.stringify(p)).join(', ')
+
+  console.warn(`Vitest encountered a \`${name}(${formatedParams})\` call that it cannot handle by default, so it returned \`${value}\`. Read more in https://vitest.dev/guide/browser#thread-blocking-dialogs.
+If needed, mock the \`${name}\` call manually like:
+
+\`\`\`
+import { expect, vi } from "vitest"
+
+vi.spyOn(window, "${name}")${defaultValue ? `.mockReturnValue(${JSON.stringify(defaultValue)})` : ''}
+${name}(${formatedParams})
+expect(${name}).toHaveBeenCalledWith(${formatedParams})
+\`\`\``)
+  return value
+}
+
+export const setupDialogsSpy = () => {
+  globalThis.alert = showPopupWarning('alert', undefined)
+  globalThis.confirm = showPopupWarning('confirm', false, true)
+  globalThis.prompt = showPopupWarning('prompt', null, 'your value')
+}

packages/browser/src/client/main.ts

@@ -7,6 +7,7 @@ import { BrowserSnapshotEnvironment } from './snapshot'
 import { importId } from './utils'
 import { setupConsoleLogSpy } from './logger'
 import { createSafeRpc, rpc, rpcDone } from './rpc'
+import { setupDialogsSpy } from './dialog'
 
 // @ts-expect-error mocking some node apis
 globalThis.process = { env: {}, argv: [], cwd: () => '/', stdout: { write: () => {} }, nextTick: cb => cb() }
@@ -71,6 +72,7 @@ ws.addEventListener('open', async () => {
   iFrame.setAttribute('src', '/__vitest__/')
 
   await setupConsoleLogSpy()
+  setupDialogsSpy()
   await runTests(paths, config)
 })