原生 Javascript Ajax 请求

/**
 * javascript request
 *
 * @param string method (POST,GET,PUT,PATCH,UPDATE,DELETE)
 * @param string url
 * @param function callback request success callback
 *
 * @see https://developer.mozilla.org/zh-CN/docs/Web/API/XMLHttpRequest
 */
function request(method, url, callback){
    var http = null;
    if(window.XMLHttpRequest){
        http = new XMLHttpRequest();
    }else if(window.ActiveXObject){
        http = new ActiveXObject("Microsoft.XMLHTTP");
    }
    http.open(method, url, true);
    http.onreadystatechange = function(){
        if(http.readyState == 4){
            if(http.status == 200){
                callback(http.responseText);
            }
        }
    }
    http.send();
}
//example
request("GET", "/api/userinfo", function(html){
    console.log(html);
});