erickoledadevrel/Code.gs

## Code.gs
function onOpen() {
  SpreadsheetApp.getUi().createMenu('Testing')
  .addItem('Show Sidebar', 'showSidebar')
  .addToUi();
}

function showSidebar() {
  var sidebar = HtmlService.createHtmlOutputFromFile('Sidebar')
  .setSandboxMode(HtmlService.SandboxMode.IFRAME)
  .setTitle('Sidebar');
  SpreadsheetApp.getUi().showSidebar(sidebar);
}

function getActiveRange() {
  return SpreadsheetApp.getActiveRange().getA1Notation();
}

## Sidebar.html
<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
  </head>
  <body>
    Active range: <span id="range"></span>
    <script src="//cdnjs.cloudflare.com/ajax/libs/visibility.js/1.2.1/visibility.min.js"></script>
    <script>
    Visibility.every(1000, function () {
      getActiveRange();
    });

    function getActiveRange() {
      console.log('Running... ' + new Date());
      google.script.run.withSuccessHandler(showRange).getActiveRange();
    }

    function showRange(range) {
      document.getElementById('range').innerHTML = range;
    }
    </script>
  </body>
</html>
	function onOpen() {
	SpreadsheetApp.getUi().createMenu('Testing')
	.addItem('Show Sidebar', 'showSidebar')
	.addToUi();
	}

	function showSidebar() {
	var sidebar = HtmlService.createHtmlOutputFromFile('Sidebar')
	.setSandboxMode(HtmlService.SandboxMode.IFRAME)
	.setTitle('Sidebar');
	SpreadsheetApp.getUi().showSidebar(sidebar);
	}

	function getActiveRange() {
	return SpreadsheetApp.getActiveRange().getA1Notation();
	}