A brief discussion on jQuery asynchronous object (XMLHttpRequest)_javascript skills

Let’s first take a look at the five steps of asynchronous objects

This is requested by post,

Copy code The code is as follows:

//1.00Create asynchronous object
          var xhr = new XMLHttpRequest();
                    //2.0
                xhr.open("post", url,params, true);
//3.0 uses the Formdata attribute to pass parameters
               xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
//4.0 Set callback function
                 xhr.onreadystatechange = function () {
If (xhr.readyState == 4 && xhr.status == 200) {
alert(xhr.responseText);
                }
            }
                                                                                                                                                                                         //5.0 passing parameters
                 xhr.send(params);

Combine the get request to create an asynchronous object package

get

in request

xhr.setRequestHeader("If-Modified-Since", "0"); is to clear the cache

And post request

Copy code The code is as follows:

xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

It’s for the transmission method
in
The type in can be obtained in three ways, including application/x-www-form-urlencoded

Copy code The code is as follows:

var ajaxHelp = {
    CreatXHR: function () {
        //创建异步对象
        var xhr = new XMLHttpRequest();
        return xhr;
    },
    //ajax的get请求
    AjaxGet: function (url, callBack) {
        this.AJaxCommon("get", url, null, callBack);
    },
    //ajax的post请求
    AjaxPost: function (url, params, callBack) {
        this.AJaxCommon("post", url, params, callBack);
    },
    AJaxCommon: function (method, url, params, callBack) {
        //1.0
        var xhr = this.CreatXHR();
        //2.0
        xhr.open(method, url, true);
        //3.0
        if (method == "get") {
            xhr.setRequestHeader("If-Modified-Since", "0");
        } else {
            xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        }
        //4.0
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4 && xhr.status == 200) {
                var datas = JSON.parse(xhr.responseText);
                //执行回调函数
                callBack(datas);
            }
        }
        //5.0
        xhr.send(params);
    }
};

ps:在JQuery里面是有$.ajax  和$.get /   $.Post  等异步请求的方法的。以前的封装就不用了。额。好扯。其实他们底层也是这样的写的呢。JQuery就是为了解决各个浏览器的兼容性问题而已

以上就是本人对于jQuery异步对象（XMLHttpRequest）的理解，如有遗漏，麻烦联系我，补充上。