Question

我读取json文件以使用req.params进行查询，我想返回res.json，但是我从express.js中得到了错误

_http_outgoing.js:482
    throw new ERR_HTTP_HEADERS_SENT('set');
    ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

在route.js中

module.exports = (app) => {
  app.get('/find/:province', province.find);
}

在controller.js中

exports.find = function (req, res) {
  fs.readFile('./app/models/province_file.json', function(err, provinces){
    if (err) throw err;
    let obj_provinces = JSON.parse(provinces);
    let province = req.params.province;
    for (var i = 0; i < obj_provinces.features.length; i++) {
      if (obj_provinces.features[i].properties.tb_tn == province) {
        let obj_result = obj_provinces.features[i].properties;
        console.log(obj_result);
        res.json(obj_result);
      }
    }
  });
}

运行代码时出现错误

_http_outgoing.js:482
    throw new ERR_HTTP_HEADERS_SENT('set');
    ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:482:11)
    at /Users/workspace/app/controllers/controller.js:87:13
    at FSReqCallback.readFileAfterClose [as oncomplete] (internal/fs/read_file_context.js:54:3)

Answer 1

请勿在for循环中调用res.json(obj_result);，让您的循环完成工作，然后调用 res.json(obj_result);;

在if res.json(obj_result)中被调用不止一次，这就是您收到此错误的原因。

最佳实践是在执行执行过程中使用return，以确保执行在此时结束。

return res.json(obj_result);

错误[ERR_HTTP_HEADERS_SENT]：在Express.js中将标头发送到客户端后，无法设置标头

1 个答案: