Auto sorting by multiple columns in Google Sheets

I have a data-set which I would like to have sorted with first column 6 and then column 7.

From this post: How can I make some data on a Google Sheets auto-sorting? I have gotten ideas about making a script.

I have made it so far it is sorting by column 6 but NOT column 7.

Any idea what I do wrong?

function myFunction() {

}
function onEdit(event){
  var sheet = event.source.getActiveSheet();
  var editedCell = sheet.getActiveCell();

  var columnToSortBy = 6;
  var tableRange = "A2:U";

  if(editedCell.getColumn() == columnToSortBy){   
    var range = sheet.getRange(tableRange);
  range.sort([{column: 6, ascending: true}, {column: 7, ascending: true}]);
  }
}