如何从react native中的函数返回值

function add(a, b) {
  return a + b;
}

const result = add(2, 3);
console.log(result); // 输出：5

function fetchData() {
  return new Promise((resolve, reject) => {
    // 异步操作，比如发送网络请求
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => resolve(data))
      .catch(error => reject(error));
  });
}

fetchData()
  .then(data => console.log(data))
  .catch(error => console.error(error));

function fetchData(callback) {
  // 异步操作，比如发送网络请求
  fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(data => callback(null, data))
    .catch(error => callback(error, null));
}

fetchData((error, data) => {
  if (error) {
    console.error(error);
  } else {
    console.log(data);
  }
});