For testing, you can write to the [log](https://developers.google.com/apps-script/guides/logging) using the syntax `console.log()`. For example, to log the `htmlListArray` we created above.
```JavaScript title="Code.gs"
function doGet(e){
var ss = SpreadsheetApp.openById(id);
var ws = ss.getSheetByName('data');
var list = ws.getDataRegion(ws).getValues();
var htmlListArray = list.map(function(r){ return '<li>' r[0] + '</li>'; }).join('');
console.log(htmlListArray);
//
}
```
For server-side logs, on the left sidebar of the App Script editor, open Executions and then expand the call to the `doGet` function (should be first in the list, hover over the entry and click the down arrow to the right).
For app-side logs, hit F12 to launch the developer console, select the Console, show the left sidebar, and select messages. Logs will be printed under 'user messages'.