怎么捕获JSONP跨域请求的连接异常? 400 报错

捕获不了的，只有用超时实现。jquery对跨域jsonp请求是没有做异常处理的。

var JSONP = (function () {
    var counter = 0,
        head, query, key, window = this;

    function load(url) {
        var script = document.createElement('script'),
        var done = false;
        script.src = url;
        script.async = true;

        script.onload = script.onreadystatechange = function () {
            if (!done && (!this.readyState || this.readyState === "loaded" || this.readyState === "complete")) {
                done = true;
                script.onload = script.onreadystatechange = null;
                if (script && script.parentNode) {
                    script.parentNode.removeChild(script);
                }
            }
        };
        if (!head) {
            head = document.getElementsByTagName('head')[0];
        }
        head.appendChild(script);
    }

    function jsonp(url, params, error, callback) {
        query = "?";
        params = params || {};
        for (key in params) {
            if (params.hasOwnProperty(key)) {
                query += encodeURIComponent(key) + "=" + encodeURIComponent(params[key]) + "&";
            }
        }
        var jsonp = "json" + (++counter);
        window[jsonp] = function (data) {
            callback(data);
            try {
                delete window[jsonp];
            } catch (e) {}
            window[jsonp] = null;
        };

        load(url + query + "callback=" + jsonp);

        error = error ||
        function () {};

        window.setTimeout(function () {
            if (typeof window[jsonp] == "function") {

                // replace success with null callback in case the request is just very latent.
                window[jsonp] = function (data) {
                    try {
                        delete window[jsonp];
                    } catch (e) {}
                    window[jsonp] = null;
                };

                // call the error callback
                error();

                // set a longer timeout to safely clean up the unused callback.
                window.setTimeout(function () {
                    if (typeof window[jsonp] == "function") {
                        try {
                            delete window[jsonp];
                        } catch (e) {}
                        window[jsonp] = null;
                    };
                }, 120000);
            };
        }, 10000);

        return jsonp;
    }
    return {
        get: jsonp
    };
}());

/*
Example:
----------------

var url = 'http://blog.eood.cn/api';
var error = function() {alert('error');};
var success = function(data) {
        // process the data
};
JSONP.get( url, {'parm1': 'parm1_value', 'parm2': 'parm2_value'}, error, success);

*/

找到一个JSONP的封装，原理还是利用超时，结贴！

$.ajaxSetup( {
    error: function(jqXHR, textStatus, errorMsg){ // 出错时默认的处理函数
        // jqXHR 是经过jQuery封装的XMLHttpRequest对象
        // textStatus 可能为： null、"timeout"、"error"、"abort"或"parsererror"
        // errorMsg 可能为： "Not Found"、"Internal Server Error"等

        // 提示形如：发送AJAX请求到"/index.html"时出错[404]：Not Found
        alert( '发送AJAX请求到"' + this.url + '"时出错[' + jqXHR.status + ']：' + errorMsg );        
    }
} );