原生javascript封装类似jquery的ajax请求跨域函数

function ajax(opt) {
    opt = opt || {};                                     // 对实参处理
    var xmlhttp, method, url, async, dataType, data;
    method = opt.method || ‘GET‘;                        // 默认method为GET
    method = trim(method).toUpperCase();                 //转换成大写并去除空格
    url = opt.url                                        //请求地址
    url = trim(url);
    async = opt.async || true;                           // 默认为异步请求
    dataType = opt.dataType || ‘HTML‘;                   // 设置跨域
    dataType = trim(dataType).toUpperCase();
    data = opt.data || {};                              // 发送参数
    function trim(str) {
        return str.replace(/^\s+|\s+$/g, "");           // 删除左右空格
    };
    var formatParams = function () {                    // 定义格式化参数函数
        if (typeof (data) == "object") {
            var str = "";
            for (var key in data) {
                str += key + "=" + data[pro] + "&";
            }
            data = str.substr(0, str.length - 1);
        }
        if (method == ‘GET‘ || dataType == ‘JSONP‘) {
            if (url.lastIndexOf(‘?‘) == -1) {
                url += ‘?‘ + data;
            } else {
                url += ‘&‘ + data;
            }
        }
    }
    if (window.XMLHttpRequest) {                       // 创建XMLHttpRequest对象
        //Chrome || Firefox
        xmlHttp = new XMLHttpRequest();
    } else {
        //IE
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    }                                        
    if (dataType == ‘JSONP‘) {                                                // 跨域请求
        if (typeof (opt.beforeSend) == ‘function‘) opt.beforeSend(xmlHttp);
        var callbackName = (‘jsonp_‘ + Math.random()).replace(".", "");
        var oHeader = document.getElementsByTagName(‘header‘)[0];
        data.callback = callbackName;
        var ele = document.createElement(‘script‘);
        ele.type = "text/javascript";
        ele.onerror = function () {
            console.log(‘failed‘);
            opt.error && opt.error("failed");
        };
        oHeader.appendChild(ele);
        window[callbackName] = function (json) {
            oHeader.removeChild(ele);
            window[callbackName] = null;
            opt.success && opt.success(json);
        };
        formatParams();
        ele.src = url;
        return;
    } else {
        formatParams();
        xmlHttp.open(method, url, async);
        xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded;charset=utf-8");     // 设置响应头
        if (typeof (opt.beforeSend) == ‘function‘) opt.beforeSend(xmlHttp);
        xmlHttp.send(data);                                       // 发送请求
        xmlHttp.onreadystatechange = function () {                 // 响应处理
            if (xmlHttp.status != 200) {
                console.log(xmlHttp.status + ‘failed‘);
                opt.error && opt.error(xmlHttp.status + ‘failed‘);
                return;
            }
            if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
                if (dataType == ‘JSON‘) {
                    try {
                        res = JSON.parse(xmlHttp.responseText);
                    } catch (e) {
                        console.log(‘json格式错误‘);
                        opt.error(‘json格式错误‘);
                    }
                } else if (dataType == ‘XML‘) {
                    res = xmlHttp.responseXML;
                } else {
                    res = xmlHttp.responseText;
                }
                opt.success && opt.success(res);
            }
        }
    }
}


//调用示例

ajax({
    url: ‘http://www.baidu.com‘,
    type: "get",
    dataType: "jsonp",
    success: function (data) {
        console.log(data);
    },
    error: function (err) {
        console.log(err);
    }
})