从源“http://localhost:3000"获取的访问已被 CORS 策略阻止

添加到数据库显示错误.我应该怎么办?

Adding to the database shows the error. what should I do?

从源 'http://localhost:3000' 访问 'http:xxx' 已被阻止CORS 策略:对预检请求的响应未通过访问控制检查:请求的资源上不存在Access-Control-Allow-Origin"标头.如果不透明响应满足您的需求，请将请求的模式设置为no-cors"以在禁用 CORS 的情况下获取资源.

Access to fetch at 'http:xxx' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

我的功能:

  addItem = (e) => {
e.preventDefault();
const ob = {
  X: 53.0331258,
  Y: 18.7155611,
}
fetch("http://xxx", {
  method: "post",
  headers: {
    "Content-Type": "application/json"
  },
  body: JSON.stringify(ob)
})
  .then(res => res.json())
  .then(res => {
    console.log(res);
  })

}