// This will run when the spreadsheet is opened or the browser page is refreshed
function onOpen() {
  SpreadsheetApp.getUi()
      .createMenu('Custom Menu')
      .addItem('HTML Vue', 'openDialog')`enter code here`
      .addToUi();
}

function openDialog() {
  var ss = SpreadsheetApp.getActive();
  var cell = ss.getActiveCell();
  var html = HtmlService.createHtmlOutput(cell.getValue());
  SpreadsheetApp.getUi().showModalDialog(html, 'HTML Vue:' );
}