json object as a variable (javascript) [duplicate]

how can I use the json object as a variable?
For example i want the age of sarah

function changeValue(jsonfile, object, value) {
  const filepath = './' + jsonfile + '.json';
  const data = JSON.parse(fs.readFileSync(filepath));
  data.object = value;
  fs.writeFileSync(filepath, JSON.stringify(object, null, 4));

  console.log(data);
}
changeValue('file.json', data.users.sarah.age, '30');
//ReferenceError: data is not defined

file.json

{
  "users": {
    "adam": {
      "age": "19",
      "gender": "male"
    },
    "sarah": {
      "age": "23",
      "gender": "female"
    },
  }
}

Thanks in advance