位置0的JSON内容中的意外令牌<错误

Question

根据jsonlint，我似乎有一个有效的JSON对象：

{"data":[{"name":"undefined - blablabla (undefined)"},{"name":"undefined - blablabla (undefined)"},{"name":"undefined - blablabla (undefined)"},{"name":"undefined - On blablabla (undefined)"}]}

但是，我遇到以下错误：

Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0

这是我的反应成分：

  componentDidMount() {
    fetch('/',    {
          method: 'GET',
          withCredentials: true,
          headers: {
    'Content-Type': 'application/json', 
    'Access-Control-Allow-Origin': '*',
    'Accept': 'application/json' },
     credentials: 'same-origin'      })
      .then(res => res.json())
      .then(user => this.setState({ data: data }));
  }

这是我从服务器端发送响应的方式：

app.get(
    "/auth/google/callback",
    passport.authenticate("google", { failureRedirect: "/error", session: false }),
    function(req, res) {
        var token = req.user.token;
    request('https://www.googleapis.com/analytics/v3/management/accounts?access_token=' + token,  
function (error, response, body) {
    let views = []
   JSON.parse(body).items.forEach(view => {
            views.push({
              name: view.webPropertyId + ' - ' + view.name + ' (' + view.websiteUrl + ')'
            })
          })
  console.log(JSON.parse(body).items);
  res.json({data:views});

});
    }
);

EDIT＃1：我用'Accept': 'application/json'

更新了标题