JavaScript Interface object
JavaScript Interface is an object Android transfers to WebView. The front end will then access this object to send messages using a callback function on Android.
JavaScript Interface structure
onGetToken(token: String): Unitmethod
This is a required method, through which a token for passing CAPTCHA verification is transferred. It is called on the front end once the service has handled a user's attempt to pass CAPTCHA verification.
onChallengeVisible(): Unitmethod
This is an optional method which you may only need to embed an invisible CAPTCHA. It is called when the invisible CAPTCHA shows a challenge to the user. By default, WebView with invisible CAPTCHA is hidden, so you need to track the moment when the WebView needs to be displayed.
onChallengeHidden(): Unitmethod
This is an optional method which you may only need to embed an invisible CAPTCHA. If the user swiped CAPTCHA off, they cannot restore it on their own; you will need to show the previous screen to the user.
Note
When creating a class, the above methods are marked with the @JavascriptInterface annotation.
If you develop your own website with CAPTCHA, you can change the names of these methods. In this case, you will need to change the method names on the front-end side, too.