js原生ajax

function Ajax(config) {
    config = Object.assign({
        url: '',
        type: 'GET',
        dataType: 'json',
        data: {}
    }, config);
    console.log(config);
    //1.创建ajax对象
    var xhr = new XMLHttpRequest() || new ActiveXObject("Microsoft.XMLHTTP");
    //2.设置回掉
    xhr.onreadystatechange = function () {
        if (xhr.readyState === 4) {
            if (xhr.status >= 200 && xhr.status <= 300) {
                config.success && config.success(xhr.responseText, xhr.responseXML)
            } else {
                config.error && config.error(xhr.status)
            }
        }
    };

    //3.连接和发送
    if (config.type === 'GET' || config.type === 'get') {
        xhr.open('GET', config.url + '?' + formatParams(config.data), true);
        xhr.send(null);
    } else if (config.type === 'POST' || config.type === 'post') {
        xhr.open('POST', config.url, true);
        //设置请求头以表单的形式提交
        xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        xhr.send(formatParams(config.data));
    }


    function formatParams(data) {
        var arr = [];
        for (var name in data) {
            arr.push(encodeURIComponent(name) + '=' + encodeURIComponent(data[name]));
        }
        arr.push("t=" + Math.random());
        return arr.join("&")
    }

}