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Find a reCAPTCHA v2 success handler in the widget’s data-callback attribute or in the callback option passed to grecaptcha.render. Google’s documented API does not let you inject an arbitrary token into the widget and make it count as a successful challenge by manually firing that callback. Calling your own handler can test your application’s client-side flow, but only server-side verification with Google establishes whether a response is valid.
How do I find the reCAPTCHA v2 callback function?
The callback is an application function you configure; it is not a universal function name built into every reCAPTCHA widget. Google documents two common places to find its name: the widget’s HTML attributes and the options supplied when rendering it with JavaScript. See Google’s reCAPTCHA v2 display and API documentation, last updated October 8, 2024.
Automatically rendered widget
Search the page markup for data-callback. For example:
<div class="g-recaptcha" data-sitekey="YOUR_SITE_KEY" data-callback="onCaptchaSuccess"></div>Here, onCaptchaSuccess is the configured function name. Search the page’s scripts for its definition. If the application uses a framework or wrapper, follow how it registers the callback; the function cannot be identified from the widget alone if its source is unavailable.
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Explicitly rendered widget
For a widget created with grecaptcha.render, inspect the options passed to that call:
const widgetId = grecaptcha.render('captcha', {
sitekey: 'YOUR_SITE_KEY',
callback: onCaptchaSuccess
});The callback option names the success handler, and grecaptcha.render returns a widget ID. Keep that ID when the page may contain multiple widgets so later API calls target the right one.
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If no success callback is configured
After the user completes a challenge, grecaptcha.getResponse(widgetId) can retrieve that widget’s response. If you omit the ID, Google’s API uses the first widget. With multiple widgets, pass the ID returned by grecaptcha.render rather than relying on the default.
For issues other than success, check data-expired-callback or expired-callback for an expired response, and data-error-callback or error-callback for an error path. An expired challenge needs renewed verification; an error callback is for handling an error such as a connectivity problem.
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Can I trigger the callback after injecting a token?
You can call an application function directly if you want to test what your own code does with a supplied string. That does not inject a valid answer into the reCAPTCHA widget, simulate a genuine challenge, or prove that Google will accept the string. The documented widget API provides callbacks for successful widget responses, but no supported method for injecting an arbitrary token and manually triggering the widget’s success callback.
Keep these two operations separate:
- Testing client-side application logic: call your application’s success-handling function with a test fixture to check downstream UI or request handling. This tests your function only.
- Verifying a reCAPTCHA response: send the response token and your secret from the server to Google’s siteverify endpoint, then make the application’s decision from Google’s verification response. Never expose the secret in browser code.
Google states that each response token is valid for two minutes and can be verified only once to prevent replay attacks. A manually supplied string does not bypass those checks or become verified merely because application code receives it.
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How do I programmatically run an invisible reCAPTCHA v2 challenge?
For an invisible v2 widget, the documented way to start the challenge programmatically is grecaptcha.execute(widgetId). This starts the challenge; it is not a substitute for receiving the completed response or verifying it on your server. The configured success callback receives the response after the challenge succeeds. See Google’s invisible reCAPTCHA documentation.
What does a supported explicit-render setup look like?
Define the API onload function before loading Google’s script. Google specifically requires that ordering and recommends async and defer for explicit rendering to avoid a load race.
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<div id="captcha"></div>
<script>
function onCaptchaSuccess(responseToken) {
// Send the response to your application server for verification.
submitResponseForServerVerification(responseToken);
}
function onCaptchaExpired() {
// Ask the user to complete the challenge again.
}
function onCaptchaError() {
// Tell the user to retry when connectivity is restored.
}
function onRecaptchaApiLoaded() {
window.captchaWidgetId = grecaptcha.render('captcha', {
sitekey: 'YOUR_SITE_KEY',
callback: onCaptchaSuccess,
'expired-callback': onCaptchaExpired,
'error-callback': onCaptchaError
});
}
</script>
<script src="https://www.google.com/recaptcha/api.js?onload=onRecaptchaApiLoaded&render=explicit" async defer></script>After a successful challenge, Google calls onCaptchaSuccess with the response token as its argument. The example’s application-specific submission function must send that response to your server, where verification takes place.
Quick Recap
Which rendering approach should I inspect?
| Approach | Where the success callback is configured | Widget ID | When it fits |
|---|---|---|---|
| Automatically rendered widget | data-callback on the widget markup |
May be omitted for a single widget; pass the ID when targeting a particular widget or working with multiple widgets. | Markup-driven setup without explicit JavaScript rendering. |
| Explicit JavaScript rendering | callback in the options passed to grecaptcha.render |
grecaptcha.render returns an ID to retain for widget-specific API calls. |
When the application needs to render or control a widget through JavaScript. |
| Invisible v2 challenge | The configured callback receives the response after success. | Pass the widget ID to grecaptcha.execute(widgetId) when starting the challenge programmatically. |
When the application needs to initiate an invisible challenge in code. |
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