Turn google spreadsheet into a JSON API

Code.gs

function doGet(request) 
{
  var spreadsheetId = 'YOUR SPREADSHEET ID HERE';
  var sheetId = request.parameters.sheet || 0;
  
  // Get data from the sheet
  var sheet = getSheet(spreadsheetId, sheetId);
  var dataArray = getData(sheet);
  
  // Normalize the headers
  var headers = dataArray.shift().map(function (header) { return normalizeName(header); })
  
  // Map rows to JSON
  var response = dataArray.map(function (row) {
    return row.reduce(function (memo, value, idx) {
      memo[headers[idx]] = value;
      return memo;
    }, {});
  });
  
  return ContentService.createTextOutput(JSON.stringify(response)).setMimeType(ContentService.MimeType.JSON)
  
}

function getSheet(spreadsheetId, sheetId)
{
  var ss = SpreadsheetApp.openById(spreadsheetId);
  return ss.getSheets()[sheetId];
}

function getData(sheet)
{
  var sheet_range = sheet.getDataRange();
  return sheet_range.getValues();
}

// Lowercase, spaces to _, strip the rest
function normalizeName (name) {
  return name.toLowerCase().replace(/ /g, '_').replace(/[^a-z0-9_-]/g, '');
}

By this, we can only get data of 1 sheet.
If we need to get more than 1 sheet data, then what needs to be changed