我看这篇文章https://segmentfault.com/a/11... 写的
代码如下

fetch(apiUrl, {
      method: "POST",
      body: JSON.stringify({ aaa: 1 }),
      headers: {
            'Content-Type': 'application/json',
      },
    });

后端php

  header("Access-Control-Allow-Origin:*");
  header("Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept");
  var_dump($_REQUEST);

结果

array(0) {
}

chrome开发工具查看request header

OPTIONS /LotteryAPP_MS/01Code/partner_react/api.php HTTP/1.1
Host: 127.0.0.1
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
Access-Control-Request-Method: POST
Origin: http://localhost:3000
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
Access-Control-Request-Headers: content-type
Accept: */*
Referer: http://localhost:3000/
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.8

没有看到Content-Type: application/json，也没有看到参数，请求变成OPTIONS而不是POST了？
我又试了一下，似乎和跨域有关？同域下的就不会这样？

加上mode:'no-cors',这样就变成可以post请求,从chrome开发者工具上看，也能看到参数和返回

fetch(apiUrl, {
      method: "POST",
      mode: 'no-cors',
      body: JSON.stringify({ aaa: 1 }),
      headers: {
            'Content-Type': 'application/json',
      },
    }).then(function(response) {
         response.text().then((r) => {
            console.log(r);
         }).catch((r) => {
            console.log(r);
         });
    }, function(error) {
         console.log(error);
    });

但是，php还是获取不到，而且php的返回，这里用response.text()也拿不到