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Listen for the dialog event on the Puppeteer Page that owns the browser interaction. The event gives you a Dialog object; inspect type(), message(), and, for prompts, defaultValue(), then explicitly await dialog.accept() or await dialog.dismiss(). For a prompt that should submit text, pass that text to accept(value).
This event is for JavaScript dialogs such as alert, confirm, prompt, and beforeunload. A modal rendered with ordinary HTML is different: select and operate on its elements with Puppeteer’s locator APIs instead of waiting for a dialog event. See the PageEvent reference, Dialog class reference, and page-interactions guide.
What Puppeteer calls a dialog
Puppeteer surfaces browser-level JavaScript dialogs through the page’s dialog event. The callback receives a Dialog instance representing the currently displayed dialog.
| Dialog type | Typical source | Response method | Important detail |
|---|---|---|---|
alert |
alert('message') |
accept() or dismiss() |
Choose the response that matches the behavior your test is meant to verify. |
confirm |
confirm('Continue?') |
accept() for proceed, dismiss() for cancel |
The intended application outcome, not a universal policy, determines the branch. |
prompt |
prompt('Name', 'Guest') |
accept(value) or dismiss() |
Use accept(value) when automation must enter text; defaultValue() exposes the displayed default. |
beforeunload |
A page asks whether to leave or close | accept() or dismiss() |
The Puppeteer API exposes the event, but the correct navigation outcome depends on the flow being tested. |
The current API references identify these four examples. Documentation pages can carry different version labels, so check the reference that matches the Puppeteer version deployed by your project.
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Inspect the Dialog object before responding
Use the object’s inspection methods to make the response explicit and auditable.
| Method or property | What it provides | When to use it |
|---|---|---|
type() |
The dialog type, such as alert, confirm, prompt, or beforeunload. |
Branch to the response required by the test case. |
message() |
The text displayed by the dialog. | Verify that the expected warning or question appeared before continuing. |
defaultValue() |
The prompt’s default text; for non-prompts it is an empty string. | Check or preserve a suggested prompt value. |
handled |
Whether the dialog has already been handled. | Avoid attempting a second response in complex asynchronous code. |
The methods and handled property are documented in the Dialog class reference.
Basic JavaScript pattern: log and dismiss
Register the listener on the relevant page, log the type and message, then resolve every dialog with an awaited response. The listener must choose a response; merely observing the event does not close the dialog.
import puppeteer from 'puppeteer';
const browser = await puppeteer.launch();
const page = await browser.newPage();
page.on('dialog', async dialog => {
console.log(dialog.type(), dialog.message());
await dialog.dismiss();
});
await page.goto('https://example.com');
// Perform the action that can show a JavaScript dialog here.
await browser.close();Puppeteer’s class example likewise logs dialog.message() and awaits dialog.dismiss(). Dismissing is only correct when cancellation is the intended result; change the response for flows that must proceed.
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Accept alerts, confirms, prompts, and beforeunload dialogs
Accept an alert
An alert has no value to enter. Call accept() and continue with the assertion or action that follows the alert.
page.on('dialog', async dialog => {
if (dialog.type() === 'alert') {
console.log('Alert:', dialog.message());
await dialog.accept();
}
});Choose a confirm branch
For a confirmation flow, encode the application outcome you want to test. Accepting represents proceeding; dismissing represents cancelling.
page.on('dialog', async dialog => {
if (dialog.type() !== 'confirm') return;
if (dialog.message() === 'Delete this item?') {
await dialog.accept();
} else {
await dialog.dismiss();
}
});Matching the message is useful when several confirmations can occur on one page. If the message is not the expected one, dismissing it is a conservative test response; use the behavior your scenario actually requires.
Enter text in a prompt
Pass the text as the optional argument to accept(value). The argument has an effect for prompts; it is ignored for other dialog types.
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page.on('dialog', async dialog => {
if (dialog.type() !== 'prompt') {
await dialog.dismiss();
return;
}
console.log('Prompt:', dialog.message());
console.log('Suggested value:', dialog.defaultValue());
await dialog.accept('value to submit');
});If the test should cancel the prompt, call dismiss() instead. The documented signature is accept(promptText?); omitting the argument accepts without replacing the prompt value. See Dialog.accept().
Handle beforeunload deliberately
A beforeunload dialog is delivered through the same event. Decide first whether the scenario is supposed to allow or prevent the navigation or close operation, then call accept() or dismiss() accordingly.
page.on('dialog', async dialog => {
if (dialog.type() === 'beforeunload') {
// Select the response required by this navigation test.
await dialog.dismiss();
return;
}
await dialog.dismiss();
});The API confirms that beforeunload is surfaced, but browser-version-specific navigation results are not universal. Assert the resulting page state in the flow you are testing rather than assuming that every browser version behaves identically.
A complete type-aware handler
This example records all available inspection data, prevents a second response when the object is already handled, and makes each policy visible in one place.
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import puppeteer from 'puppeteer';
const browser = await puppeteer.launch();
const page = await browser.newPage();
page.on('dialog', async dialog => {
if (dialog.handled) return;
const type = dialog.type();
const message = dialog.message();
const defaultValue = dialog.defaultValue();
console.log({ type, message, defaultValue });
switch (type) {
case 'prompt':
if (message === 'Project name?') {
await dialog.accept('demo-project');
} else {
await dialog.dismiss();
}
break;
case 'confirm':
await dialog.accept();
break;
case 'alert':
await dialog.accept();
break;
case 'beforeunload':
// Pick accept or dismiss for the navigation scenario under test.
await dialog.dismiss();
break;
default:
await dialog.dismiss();
}
});
await page.goto('https://example.com');
// Trigger the page action that opens a dialog.
await browser.close();Use one policy per test scenario. Blindly accepting every type can submit an unintended prompt value or approve a destructive confirmation; blindly dismissing can prevent the path you intended to verify.
JavaScript dialogs versus HTML modals
Visual appearance is not enough to identify a browser dialog. A site can render a custom modal with ordinary HTML, CSS, and JavaScript. Such a modal does not emit Puppeteer’s dialog event.
Symptoms of a DOM modal
- Your action visibly opens a modal, but the
dialoglistener never runs. - The modal has inspectable buttons, inputs, and containers in the page DOM.
- The page’s controls can be selected with normal locator APIs.
How to handle it
Inspect the modal’s DOM and interact with it as a page element: locate its input, fill it, and click its confirm or cancel button. Puppeteer’s page-interactions guide recommends locator APIs for ordinary element selection and interaction. Do not wait indefinitely for a JavaScript dialog event when the interface is an in-page component.
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Attach the listener before the trigger
Set up the page listener before clicking, navigating, or evaluating code that can open the dialog. This keeps the response policy in place when the event is emitted and avoids a flow that reaches a dialog with no handler.
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Always await the response
accept() and dismiss() are asynchronous methods. Await the chosen method so the rest of the test runs after Puppeteer has resolved the dialog.
Keep the policy close to the scenario
Use the message and type to distinguish multiple dialogs. Record the message when diagnosing failures, but do not rely on a message-independent “always accept” rule unless that is genuinely the behavior under test.
Check the deployed API version
The official pages currently show version labels including 25.12.0 for the PageEvent, Page interactions, and Dialog references, while the accept-method page displays 25.11.0. These labels are documentation versions, not a guarantee about the package installed in your project. Use the API reference corresponding to your deployed Puppeteer version.
Troubleshooting dialog automation
| Symptom | Likely cause | Fix |
|---|---|---|
No dialog event arrives. |
The site uses an HTML modal rather than a JavaScript dialog. | Inspect the DOM and handle the modal with locator-based element interactions. |
| The test stops after the page action. | The handler observed the event but never resolved it. | Await either dialog.accept() or dialog.dismiss() on every branch. |
| Prompt text is not entered. | The code called accept() without a value, or the dialog is not a prompt. |
Check type() and call accept('text') for a prompt. |
| An unexpected action is approved. | A global handler accepts every confirmation or alert. | Branch on type() and, where appropriate, message(); encode the intended outcome. |
| A second response throws or behaves inconsistently. | Multiple asynchronous paths attempted to handle the same object. | Check dialog.handled and centralize the response policy. |
Navigation results differ around beforeunload. |
The desired outcome depends on the browser and navigation scenario. | Choose the response deliberately and assert the resulting page state instead of assuming a universal result. |
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cURL
See the ScreenshotNeo documentation for all parameters.
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import requests
r = requests.get(
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params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
open("shot.webp", "wb").write(r.content)Node.js
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