webViewClientのonReceivedErrorとかを使う。 webViewClient

public class MainActivity extends Activity{
 
  WebView webview = new WebView(this);
  setContentView(webview);
  webview.loadUrl("http://example.com/");
 
  webview.setWebViewClient(new webViewClient(){
  @Override
    public void onReceivedError(WebView view, int errorCode, String description, String failingUrl){
 
      Log.e("Log", "errorCode: " + String.valueof(errorCode));
      Log.e("Log", "description: " + description);
      Log.e("Log", "failingUrl: " + +failingUrl);
    }
  });
}
}

JavaScriptのコンソール出力をLogcatに出す

ActivityでJavascriptを実行可に設定

WebView webview =new WebView(this);
webview.getSettings().setJavaScriptEnabled(true);
setContentView(webview);

javascript内でconsole.logを

<script>
  console.log('test!!');
</script>

端末によってはconsole.logが使えない場合があるみたいなのでこっちもあり。

onConsoleMessage

webview.setwebChromeClient(new WebChromeClient(){
  publicvoid onConsoleMessage(String message, int lineNunber, String sourceID){
    Log.d("message", message);
    Log.d("line", String.valueOf(lineNumber));
    Log.d("URL", sourceID);
  }
})