Google Sheets "sheetExists" function (detect if sheet exists)

Code.gs

function sheetExists(sheetName) {
  if (typeof sheetName !== "string") {
    throw ("The sheetExists function requires string input.")
  }
  var allSheets = SpreadsheetApp.getActive().getSheets();
  var foundSheet = false;
  var len = allSheets.length;
  var chkThisIndex = 0;
  while (!foundSheet && chkThisIndex < len) {
    if (allSheets[chkThisIndex].getName() === sheetName) {
      foundSheet = true;
    } else {
      chkThisIndex++
    }
  }
  return foundSheet;
}