无法在'XMLHttpRequest'Syncronous上执行'send' [英] Failed to execute 'send' on 'XMLHttpRequest' Syncronous

问题描述

我正在尝试通过JS通过简单的get请求连接谷歌，而且似乎总是给我同样的错误。

I'm trying to connect to google with a simple get request through JS and it seems to always be giving me the same error.

执行失败发送'on'XMLHttpRequest'：无法加载' http://google.com '。

"Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'http://google.com'."

任何线索为什么会发生这种情况？相关代码如下。

Any clue why this would be happening? Relevant code is below.

        var xmlHttp = new XMLHttpRequest();
        xmlHttp.open("GET", "http://google.com", false);
        try {
            xmlHttp.send();
        } catch (err) {
            alert("EXCEPTION: " + err.message);
        }
        alert("here's the result of the get: " + xmlHttp.responseText);

推荐答案

这只是一个跨域权限失败，到期到同源政策。如果您异步运行同一个请求并在控制台中查看，则会看到更有用的错误消息：

This is simply a cross-origin permission failure, due to the same origin policy. If you ran this same request asynchronously and looked in your console, you'd see the much more helpful error message:

XMLHttpRequest无法加载< a href =http://google.com/ =nofollow> http://google.com/ 。请求的资源上不存在Access-Control-Allow-Origin标头。因此，不允许访问来源' http：// [whatever] 。

XMLHttpRequest cannot load http://google.com/. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://[whatever]' is therefore not allowed access.

这是因为只有在 http://www.google.com 的网页上运行的脚本才能从<$ c中读取资源$ C> http://www.google.com 。如果正在获取的资源提供了适当的CORS头（例如， Access-Control-Allow-Origin ），则不会看到此错误。 （但是， http://www.google.com 不提供此类标题。）

This is because only scripts run on pages from http://www.google.com may read resources from http://www.google.com. If the resource being fetched served appropriate CORS headers (e.g., Access-Control-Allow-Origin), you would not see this error. (However, http://www.google.com serves no such headers).

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