ajax 请求封装

ajax.js

var Ajax = (function() {
    var methodsList = ['get', 'post', 'head', 'options', 'put', 'connect', 'trace', 'delete'];

    /**
     * Ajax
     * @param {String}   url
     * @param {Function} callback
     * @param {Object/String}   data
     * @param {Object}   options
     *
     */
    function Ajax(url, callback, data, options) {
        // 顺序：new XHR --> onreadystatechange ---> open() ---> other callback or property ---> send()
        var xhr = (function() {
            // 使用 typeof 不会报错
            if (typeof XMLHttpRequest !== undefined) {
                return new XMLHttpRequest();
            } else if (typeof ActiveXObject !== undefined) {
                if (typeof arguments.callee.activeXString !== 'string') {
                    var versions = ['MSXML2.XMLHttp.6.0', 'MSXML2.XMLHttp.3.0', 'MSXML2.XMLHttp'],
                        i, len;
                    for (i = 0, len = versions.length; i < len; i++) {
                        try {
                            new ActiveXObject(versions[i]);
                            arguments.callee.activeXString = versions[i];
                            break;
                        } catch (error) {
                            console.log('Your Browser do not support ' + versions[i] + '.');
                        }
                    }
                }
                return new ActiveXObject(arguments.callee.activeXString);
            } else {
                throw new Error('没有可用的 AJAX 对象构造器');
            }
        })();

        xhr.onreadystatechange = function() {
            if (xhr.readyState === 4) {
                try {
                    if ((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304) {
                        if (callback) {
                            callback(xhr.responseText, xhr.status, xhr);
                        } else {
                            console.log(xhr);
                        }
                    } else {
                        console.error('请求错误: ' + xhr.status + ' ' + xhr.statusText);
                    }
                } catch (error) {
                    console.error('回调函数内部发生错误，请检查回调函数！');
                }
            }
        };

        var method = (options && options.method && methodsList.indexOf(options.method.toLowerCase()) + 1) ? options.method : 'get';

        if (method.toLowerCase() === 'get') {
            if (typeof data === 'object' && data !== null) {
                url = (function() {
                    var queryArr = [];
                    for (var prop in data) {
                        if (data.hasOwnProperty(prop)) {
                            queryArr.push(encodeURIComponent(prop) + '=' + encodeURIComponent(data[prop]));
                        }
                    }
                    return (url + '?' + queryArr.join('&'));
                })();
                data = null;
            } else if (typeof data === 'string') {
                data = data.indexOf('?') === 0 ? data : '?' + data;
                url = url + data;
                data = null;
            } else {
                data = null;
            }
        } else {
            // 对于 POST，data 可以是null、字符串、文件（表单文件控件取得）、FormData、ArrayBuffer
            if (data instanceof FormData || data instanceof File || data instanceof ArrayBuffer) {
                data = data;
            } else if (typeof data === 'object') {
                data = function() {
                    var serializeArr = [];
                    for (var prop in data) {
                        if (data.hasOwnProperty(prop)) {
                            serializeArr.push(encodeURIComponent(prop) + '=' + encodeURIComponent(data[prop]));
                        }
                    }
                    return serializeArr.join('&');
                }();
            } else if (typeof data === 'string') {
                data = data;
            } else {
                data = null;
            }
        }

        var ifAsync = (options && options.async && options.async === false) ? false : true;

        try {
            xhr.open(method, url, ifAsync);
            // defining onload, onprogress, error and withCredentials
            (function() {
                for (var prop in options) {
                    if (options.hasOwnProperty(prop)) {
                        if (prop === 'onload') {
                            xhr.onload = function() {
                                if ((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304) {
                                    options[prop].call(xhr, xhr.responseText, xhr.status, xhr);
                                } else {
                                    console.log('load event -- Request was unsuccessful: ' + xhr.status);
                                }
                            };
                        } else if (prop === 'onprogress' || prop === 'ontimeout' || prop === 'onerror' || prop === 'onabort' || prop === 'onloadstart' || prop === 'onloadend') {
                            xhr[prop] = function(e) {
                                options[prop].call(xhr, e, xhr.responseText, xhr.status, xhr);
                            }
                        } else if (prop === 'timeout' || prop === 'withCredentials') {
                            xhr[prop] = options[prop];
                        } else if (prop === 'overrideMimeType') {
                            xhr.overrideMimeType(options[prop]);
                        } else if (prop === 'requestHeader') {
                            for (var header in options[prop]) {
                                if (options[prop].hasOwnProperty(header)) {
                                    xhr.setRequestHeader(header, options[prop][header]);
                                }
                            }
                        } else if (prop === 'upload') {
                            // 使用 Ajax 上传数据的状态事件回调函数，可用 upload.onprogress 实现上传进度条，当然需要服务器支持返回上传进度
                            for (var uploadEvent in options[prop]) {
                                if (options[prop].hasOwnProperty(uploadEvent)) {
                                    xhr.upload[uploadEvent] = options[prop][uploadEvent];
                                }
                            }
                        }
                    }
                }
            })();

            xhr.send(data);
        } catch(e) {
            console.error('可能由于跨域限制，导致无法发起 Ajax 请求。');
            xhr = null;
        }

        return xhr;
    }

    Ajax.get = function (url, callback, data, options) {
        if (options) {
            options.method = 'get';
        } else {
            options = {
                method: 'get'
            }
        }

        return Ajax(url, callback, data, options);
    };

    // 如果使用 POST 上传的是文本数据，请在 options 内设置 {requestHeader: {'Content-Type': 'application/x-www-form-urlencoded'}}
    Ajax.post = function (url, callback, data, options) {
        if (options) {
            options.method = 'post';
        } else {
            options = {
                method: 'post'
            }
        }

        data = data ? data : '';

        if (typeof data === 'string' || data.constructor === Object) {
            if (options.requestHeader) {
                options.requestHeader['Content-Type'] = 'application/x-www-form-urlencoded';
            } else {
                options.requestHeader = {
                    'Content-Type': 'application/x-www-form-urlencoded'
                }
            }
        }

        return Ajax(url, callback, data, options);
    };

    Ajax.getJSON = function (url, callback, data, options) {
        var newCallback = function (responseText, status, xhr) {
            try {
                var responseJSONObj = JSON.parse(responseText);
                if (callback) {
                    callback(responseJSONObj, status, xhr);
                } else {
                    console.log(xhr);
                }
            } catch(e) {
                console.error('数据不符合要求，无法转为 JSON 对象！请确保接口返回数据为 JSON 格式。');
            }
        };

        return Ajax(url, newCallback, data, options);
    }

    return Ajax;
})();

// 所有事件与callback都接受三个参数：responseText, status, xhr
// var callback = function(responseText, status, xhr) {
//     //...
// };

// var options = {
//     method: 'get',
//     async: false,
//     timeout: 2000,
//     ontimeout: ontimeout,
//     onerror: onerror,
//     onabort: onabort,
//     onprogress: onprogress,
//     onload: onload,
//     onloadstart: onloadstart,
//     onloadend: onloadend,
//     onprogress: onprogress,
//     withCredentials: true,
//     requestHeader: {
//          xxx: yyy,
//          ...
//     },
//     upload: {
//          onloadstart: xxx
//          onloadend: xxx
//          onprogress: xxx
//     }
//     //...
// };

// 如果使用 POST 上传的是文本数据，请在 options 内设置 {requestHeader: {'Content-Type': 'application/x-www-form-urlencoded'}}
// Ajax(/* ... */);
// new Ajax(/* ... */);
// Ajax.get(/* ... */);
// Ajax.post(/* ... */);
// Ajax.getJSON(/* ... */));

onerror和ontimeout 应该如何定义呢，我写的

 var options = {
    method: 'get',
    async: false,
    timeout: 2000,
    ontimeout: function() {
        showAlterMsg('网络状况不佳，请重试');
    },
    onerror: function () {
        showAlterMsg('请求错误，请重试');
    }
};

每次都直接执行了