title: Flutter webview with custom javascriptInterfaceAdapter or invoke JS using webview controller
body: <p>I have an old java project that performs in andorid webview with addJavascriptInterface</p>
  <pre><code>mWebView.addJavascriptInterface(new JavascriptAdapter(), &quot;AndroidFunctions&quot;);
  </code></pre>
  <p>Within <code>JavascriptAdapter</code> class there is several <code>@JavascriptInterface</code> functions. as example</p>
  <pre><code>class JavascriptAdapter {
      @JavascriptInterface
      getMacAddress(){
          DeviceInfo deviceInfo = new DeviceInfo(activity);
          return deviceInfo.getMacAddress();
    }
  }
  </code></pre>
  <p>now after opening the webview within android applications, using JS we can access that function like this way -</p>
  <p><code>var strMacAddress = AndroidFunctions.getMACAddress();</code></p>
  <p>Now I would like to achieve this thing on flutter. for that, I am using the flutter inAppWebview plugin.</p>
  <p>also, I have tried flutter_webview, WKWebview.</p>