ESP3D-WEBUI/extensions_samples/capabilities.html

<script type="text/javascript">
  function sendMessage(msg){ 
      window.parent.postMessage(msg, '*');
  }

  function processMessage(eventMsg){
        if (eventMsg.data.type  && (!eventMsg.data.id||eventMsg.data.id=="infopanel")){
            if (eventMsg.data.type=="capabilities"){
                const line =  eventMsg.data.content
                const resultPanel = document.getElementById("output");
               
                    resultPanel.innerHTML = resultPanel.innerHTML + "<br>"+ JSON.stringify(line.response, " ", "<br>")+"</span><br><hr />";
                           
            }
        }
    }


  window.onload = (event) => {
    window.addEventListener("message", processMessage, false);
  }
    
</script>

<div class="container">
    <button class="btn m-1" onclick="sendMessage({type:'capabilities', target:'webui', id:'infopanel',});">Capabilities</button>
    <div class="container m-2" id="output">
    </div>
</div>