js的post请求参数为空

fetch('https://example.com/api/data', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({ key1: 'value1', key2: 'value2' })
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));

var xhr = new XMLHttpRequest();
xhr.open('POST', 'https://example.com/api/data', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.onreadystatechange = function () {
  if (xhr.readyState === 4 && xhr.status === 200) {
    console.log(JSON.parse(xhr.responseText));
  }
};
xhr.send(JSON.stringify({ key1: 'value1', key2: 'value2' }));

axios.post('https://example.com/api/data', {
  key1: 'value1',
  key2: 'value2'
})
.then(function (response) {
  console.log(response.data);
})
.catch(function (error) {
  console.log(error);
});