dialog.html

<!DOCTYPE html>
<html>
<head>
  <link rel="stylesheet" href="https://ssl.gstatic.com/docs/script/css/add-ons.css">
  <script>
 
  function openDialog(){
     google.script.run.showPicker();
  }
  
  function getProperties(){
    google.script.run
      .withSuccessHandler(fillBox)
      .withFailureHandler(showError)
      .getProperty("name");
  }
  function fillBox(theText){
    document.getElementById('fileName').value = theText;
  }
  
  function showError(err){
    console.log(err);
    window.alert("An error has occured: " & err);
  }
  
  </script>
</head>
<body onload = "getProperties()">
  <div>
     <button onclick='openDialog()'>Open Dialog</button>
     <input type="text" id="fileName"><br>
     <p id='result'></p>
  </div>
  <script src="https://apis.google.com/js/api.js?onload=onApiLoad"></script>
</body>
</html>