用javascript修改后，如何将自定义字段的值保存到wordpress的user_meta中？

add_user_meta( $user_id, 'custom_field_name', 'custom_field_value' );

fetch('/wp-json/wp/v2/users/' + userId, {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-WP-Nonce': wpApiSettings.nonce // 需要在WordPress的页面中将wpApiSettings对象传递给JavaScript
  },
  body: JSON.stringify({
    meta: {
      custom_field_name: customFieldValue
    }
  })
})
.then(response => response.json())
.then(data => {
  // 处理保存成功后的逻辑
})
.catch(error => {
  // 处理保存失败后的逻辑
});

add_action( 'rest_api_init', function () {
  register_rest_route( 'custom/v1', '/save_custom_field/(?P<id>\d+)', array(
    'methods' => 'POST',
    'callback' => 'save_custom_field',
    'permission_callback' => function () {
      return current_user_can( 'edit_users' ); // 只允许具有编辑用户权限的用户访问
    }
  ) );
} );

function save_custom_field( $request ) {
  $user_id = $request['id'];
  $custom_field_value = $request['meta']['custom_field_name'];

  update_user_meta( $user_id, 'custom_field_name', $custom_field_value );

  return array(
    'success' => true,
    'message' => 'Custom field saved successfully.'
  );
}