fetch 使用及如何接收JS传值

fetch('https://mywebsite.com/endpoint/', {
 method: 'POST',
 headers: { 'Accept': 'application/json', 'Content-Type': 'application/json'},
 body: JSON.stringify({ username: 'username', password: 'password'})
 }).then(function(res){
 console.log(res)
 })

headers: {'Content-Type': 'application/x-www-form-urlencoded'},

body:'username='+uname+'&password='+password

input('username')

$arr = file_get_contents("php://input");

$result=array();
 foreach (explode('&', $arr) as $t){
 list($a,$b)=explode('=', $t);
 $result[$a]=$b;
 }

$result['username']