没有'Access-Control-Allow-Origin'标头错误 - 但它在那里

Question

你好，我环顾四周，尝试了几件事，无法正常工作。

我有此提取请求：

  index = () => {
    return fetch(`${baseUrl}api/deliveries`, {
      method: 'GET',
      headers: new Headers({
        'Access-Control-Allow-Origin': 'http://localhost:3000',
        'Content-Type': 'application/json',
      }),
    })
      .then(res => res.json());
  }

我在控制台中遇到此错误：

Failed to load http://localhost:8000/api/deliveries: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access. The response had HTTP status code 404. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

错误状态'Access-Control-Allow-Origin'不存在。但它是。它在那里。

有什么想法？

Answer 1

您不需要发送此标头，需要在服务器的响应中存在。

Answer 2

它应该在服务器上的选项请求的响应中，如错误消息所说。