Question

以下代码适用于Dartium，但在浏览器中转换为JavaScript时则无效：

import 'dart:html';

var getReq = "http://127.0.0.1:8080/programming-languages";

void main() {
  HttpRequest.getString(getReq).then((results) {
    query("#text").text = results;
  }).catchError((e) {
    print("Oops! Encountered $e");
  });
}

返回的错误是：

ERROR: Instance of 'Interceptor'

我正在关注JSON Web Service教程，完整来源的git repo是dartlang_json_webservice。

我使用的是Dart SDK版本0.7.2.1_r27268。

Answer 1

您的代码在Dartium和Chrome中都适用于我。

然而，当我关闭服务器时，我得到了完全相同的错误。我用chrome检查了控制台：

XMLHttpRequest cannot load http://127.0.0.1:8080/programming-languages. 
Origin http://127.0.0.1:3030 is not allowed by Access-Control-Allow-Origin. 
testhttpreq.html:1 Oops! Encountered Instance of 'Interceptor'

如果您在dart中运行此程序，则此错误类似于您收到的错误

XMLHttpRequest cannot load http://127.0.0.1:8080/programming-languages. 
No 'Access-Control-Allow-Origin' header is present on the requested resource. 
Origin 'http://127.0.0.1:3030' is therefore not allowed access.
Oops! Encountered Instance of 'HttpRequestProgressEvent'

在JavaScript中生成的toString（接收者是HttpRequestProgressEvent）：

$.toString$0 = function(receiver) {
 return $.getInterceptor(receiver).toString$0(receiver);
};

Answer 2

问题是服务器返回的CORS标头无效：

/**
 * Add Cross-site headers to enable accessing this server from pages
 * not served by this server
 * 
 * See: http://www.html5rocks.com/en/tutorials/cors/ 
 * and http://enable-cors.org/server.html
 */
void addCorsHeaders(HttpResponse res) {
  res.headers.add("Access-Control-Allow-Origin", "*, ");
  res.headers.add("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
  res.headers.add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
}

更换：

res.headers.add("Access-Control-Allow-Origin", "*, ");

使用：

res.headers.add("Access-Control-Allow-Origin", "*");

的工作原理。有关更多信息，请参阅Origin is not allowed by Access-Control-Allow-Origin。

dart：HTTPRequest在JS中不起作用，但在Dartium中起作用

2 个答案: