VaadinJSExtension.java

window.com_github_mcollovati_vaadin_MyExtension = function() {
    var me = this;
    var btn = me.getElement(me.getParentId());
    btn.onclick = function() {
      // call external lib with extension callback
      externalLib.doSomething(me.myCallback);
    }
}


@JavaScript("myextension.js", "externallib.js")
public class MyExtension extends AbstractJavaScriptExtension {

    private MyExtension(AbstractClientConnector target) {
        super(target);
        addFunction("myCallback", args -> {
          // Do something with callack args
        });
    }

    static MyExtension extend(Button button) {
        return new MyExtension(button);
    }
}


public class MyUI extends UI {
  protected void init(VaadinRequest vaadinRequest) {
     ...
    Button copy = new Button("Do something");
    MyExtension.extend(copy);     
     ...
  }
}