원생 JS AJAX 실현

function ajax(options) {
    options = options || {};
    options.type = (options.type || "GET").toUpperCase();
    options.async = options.async || true;
    var params = formatParams(options.data);
    // IE9  ，  ES5，              
    //var qs = Object.keys(data).reduce(function(pre,cur,index){
    //   return pre + '&' + encodeURIComponent(cur) + '=' + encodeURIComponent(data[cur]);
    //},'');
    //var params = qs.slice(1);

    //  xhr -  IE6/IE6         
    var xhr = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');

    //   -    
    xhr.onreadystatechange = function() {
        if (xhr.readyState == 4) {
            var status = xhr.status;
            if (status >= 200 && status < 300) {
                options.success && options.success(xhr.responseText, xhr.responseXML);
            } else {
                options.fail && options.fail(status);
            }
        }
    }

    //        -    
    if (options.type == "GET") {
        xhr.open("GET", options.url + "?" + params, options.async);
        xhr.send(null);
    } else if (options.type == "POST") {
        xhr.open("POST", options.url, options.async);
        //            
        xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        xhr.send(params);
    }
}
//     
function formatParams(data) {
    var arr = [];
    for (var name in data) {
        arr.push(encodeURIComponent(name) + "=" + encodeURIComponent(data[name]));
    }
    arr.push(("v=" + Math.random()).replace(".", ""));
    return arr.join("&");
}

//    
ajax({
    url: "url",              //    
    type: "POST",                       //    
    data: { a: "test", b: "t" },        //    
    success: function (response, xml) {
        //            
    },
    fail: function (status) {
        //            
    }
});