javascript - 没有“Access-Control-Allow-Origin”标头存在错误？

Question

我的反应应用程序中有下一个 ajax 请求 usnig jquery，这是这个请求：

index.js

$.ajax({
  type: "POST",
  url : 'http://localhost/my-app/server/send.php',
  "async": true,
  "crossDomain": true,
  "headers": {
    "accept": "application/json",
    "Access-Control-Allow-Origin":"*"
  }
}, function(data) {
  alert(data, "success!")
})

发送.php

<?
header("Access-Control-Allow-Origin: *");
echo "...response...";

但是我的 ajax 调用在控制台中引发了一个错误：

Access to XMLHttpRequest at 'http://localhost/my-app/server/send.php' 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

但是我发送标题，有什么问题？

标签： javascriptphpreactjsajax