对预检请求的响应没有't pass access control check. No '访问 - 控制 - 允许 - 原点' header is present on the requested resource. Origin ' http://localhost:3000 ' is therefore not allowed access. The response had HTTP status code 522. If an opaque response serves your needs, set the request'模式到'no-cors'以获取禁用CORS的资源 . 将'http://localhost:3000 ' is therefore not allowed access. The response had HTTP status code 522. If an opaque response serves your needs, set the request'模式发送到'no-cors'以获取禁用CORS的资源 .

如何向json添加请求标头？

var options = {
        body: info,
        type: 'json'
    }

然后`

doGetCall(url, options = {}) {
let callOptions = {
  method: 'GET'
}
callOptions.headers = {
  'Content-Type': 'application/json',
  'Access-Control-Allow-Origin': 'http://localhost:3000'
}

return this.doCall(url, callOptions);

}

最后

doCall(url, options) {
if (!options.noauth) {
  options.headers = options.headers || {};
  options.headers.Authorization = 'Bearer ' + Account.token;
}
return fetch(url, options).then(response => response.json());

}

这没有用 . 请求标头包含：

访问控制请求报头：存取控制允许来源，授权，内容类型

但没有Access-Control-Allowed-Origin标头 . 如何添加 Headers ？

json cors