是否可以区分网络错误和交叉源错误?

您可能不需要发出xhr请求来知道何时会发生交叉源错误。根据jquery的 $.get 以下内容:

var xhr = {
    get: function(url, data, callback, dataType) {
        if ( !this.isSameOrigin(url) ) {
            callback(null, "Same-origin error or whatever", null);
        }

        $.get(url, data, callback, dataType);
    },

    isSameOrigin: function(url) {
        // Do a string comparison against window.location.  Get as complicated 
        // as you'd like
        return !!(
            // Url doesn't contain a valid protocol (relative to domain))
            !url.match(/^https?:\/\//i) || 
            // Url contains a protocol but the request is to the current domain
            url.match(new RegExp("^https?://" + window.location.host, "i"))
        );
    }
};