README.md

IN ANDROID JAVA CLASS

#1 create class WebInterFace

	public class WebInterFace {
        @JavascriptInterface
        public void showToast() {
            Toast.makeText(MainActivity.this, "Toast from js", Toast.LENGTH_SHORT).show();
        }
    }

#2 make Webview with interface

looking at toaskAction, the toast key much be equal/ match with javascript function on your html page.

@SuppressLint({"SetJavaScriptEnabled", "AddJavascriptInterface"})
private void setupWebView(String webLink) {
    webView.getSettings().setJavaScriptEnabled(true);
    webView.addJavascriptInterface(new MyJavaScriptInterface(), "HTMLOUT");
    webView.addJavascriptInterface(new MyJavaScriptInterface(), "HTMLOUT2"); // add new JSInterFace rồi
    webView.addJavascriptInterface(new WebInterFace(), "toaskAction");

    webView.setWebViewClient(new WebViewClient() {
        public void onPageFinished(WebView view, String url) {
            setMyJavascripts();
        }
    });
    webView.loadUrl(webLink);

}

IN THE HTML

#1 You have a simple html page with button

<button onclick="androiToast()">Android Toast</button>

#2 and in create function androiToast() just call the toastKey like this:

 <script>
function androiToast() {
        toaskAction.showToast();

        }
</script>

notice :

You can do anything with Javascript Interface when button clicked in function showToast() of class WebInterFace in the top of this README

Demo https://youtu.be/3wHA3dh8k-g