如何在javascript中读取C# HttpResponseMessage中的内容？

public HttpResponseMessage GetContent()
{
    // 创建要返回的内容
    var content = new StringContent("Hello, world!");

    // 创建HttpResponseMessage对象并设置内容
    var response = new HttpResponseMessage(HttpStatusCode.OK);
    response.Content = content;

    return response;
}

var xhr = new XMLHttpRequest();
xhr.open('GET', '/api/content', true);
xhr.onreadystatechange = function () {
  if (xhr.readyState === 4 && xhr.status === 200) {
    var response = JSON.parse(xhr.responseText);
    console.log(response); // 获取到的内容
  }
};
xhr.send();

fetch('/api/content')
  .then(response => response.text())
  .then(data => {
    console.log(data); // 获取到的内容
  });