使用AJAX HTTP请求检索"favicon.ico"图像时出现问题 [英] Trouble on retrieving 'favicon.ico' images using AJAX HTTP requests

问题描述

我正在使用Ruby on Rails v3.0.9和jQuery 1.6.我正在尝试从某些网站检索并显示收藏夹图像.

I am using Ruby on Rails v3.0.9 and jQuery 1.6. I am trying to retrieve and display the favicon image from some web sites.

例如，为了对单个网站执行此操作，我使用以下代码:

For instance, in order to do that for a single web site I am using the following code:

$jQ.ajax({
  type:    'GET',
  url:     'http://www.facebook.com/favicon.ico',
  data:    '',
  error:   function(jqXHR, textStatus, errorThrown) {
    $jQ('#facebook_favicon').replaceWith('ERROR');
  },
  success: function(data, textStatus, jqXHR) {
    $jQ('#facebook_favicon').replaceWith("<img width='16px' height='16px' src='http://www.facebook.com/favicon.ico' />");
  }
});

我使用上面的代码执行HTTP请求，以检查是否找到了favicon:如果这样(在成功上)，它将用与HTML标记相关的#facebook_favicon替换为刚刚找到的favicon.ico图片，否则它将替换为ERROR文字.

I use the above code that performs an HTTP request in order to check if the favicon was found: if so (on success), it will replace the #facebook_favicon related to an HTML tag with the just found favicon.ico image otherwise it will replace that with an ERROR text.

但是，当我加载放置上述JavaScript的页面并检查Firebug控制台时，会得到以下信息:

However, when I load the page where the above JavaScript is placed and I inspect the Firebug Console I get the following:

这表示请求已成功执行(HTTP状态代码均为200，但Gmail除外)，但成功后我无法显示图标图像. 为什么?有什么问题吗?

It means that the request was successfully performed (HTTP status codes are all 200, except for Gmail) but I can not display the icon image on success. Why? What is the problem?

我注意到在Firebug中，响应都是空白的，就像这样:

I noted that in Firebug Responses are all blank, like this:

我该怎么做才能完成我想做的事情(我主要是指检查是否找到了网站收藏夹图标)?

What I can do to accomplish what I would like to make (I am referring mostly to check if a web site favicon is found)?

如果我使用类似以下的代码，则可以使用，但不会检查网站图标的存在:

If I use code like the following it will work but it doesn't check the favicon presence:

$jQ('#facebook_favicon').replaceWith("<img width='16px' height='16px' src='http://www.facebook.com/favicon.ico' />");

推荐答案

您不能对与当前页面不在同一域/端口/协议中的URL进行XmlHttpRequest.

You can't do XmlHttpRequests on URLs that are not on the same domain/port/protocol than the current page.

但是，您可以使用Image对象以及onload和onerror事件来检查图像是否存在:

You can, however, check that an image exists by using an Image object and the onload and onerror events:

var img = new Image;
var src = 'http://www.facebook.com/favicon.ico';
img.onload = function() {
    // the image exists, display it
};
img.src = src;

您可以将其包装在函数中

You can wrap this in a function:

function imageExists(src, callback) {
    var img = new Image;
    img.onload = function() {
        callback(src, true);
    };
    img.onerror = function() {
        callback(src, false);
    };
    img.src=src;
}

并像这样使用它:

imageExists('http://www.facebook.com/favicon.ico', function(src, exists) {
    if (exists) {
        $('body').append('<p>The image loaded correctly!</p>');
        $('<img>').attr('src', src).appendTo('body');
    } else {
        $('body').append('<p>oops, error</p>');
    }
});

在此处进行测试: http://jsfiddle.net/YpBsJ/2/

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