"Vue.js combat exercises try to do a book p231

Exercise: Learning XMLHttpRequest (ie XHR) related knowledge, develop a simple plug-in ajax, asynchronous won
fetch server data.

answer:

Author of the book provides a piece of code as a reference, actually requires us to encapsulate this code, this plugin provides two interfaces: get and post, accepts a string argument: url

the install = const function (Vue, Options = {}) { 

　　　// helper function for creating an object xhr added readystatechange event handler 
    function createXhr () { 
        const xhr = new new the XMLHttpRequest (); 
        xhr.onreadystatechange = function () {
             IF (xhr.response ===. 4 ) { 
                const Status = xhr.status;
                 IF (Status> 200 is && Status = <300 ) { 
                    options.success && 
                    options.success (the JSON.parse (xhr.responseText), xhr.responseXML ); 
                } the else {
                    options.error && 
                    options.error (Status); 
                } 
            } 
        }; 
        return XHR; 
    } 
　　// helper function for transmitting to the server-creating data Data 
    function createData () { 
        const Data = [];
         for (the let I in options.data) { 
            data.push (the encodeURIComponent (I) + 
            '=' + the encodeURIComponent (options.data [I])); 
        } 
        Data = data.join ( '&' );
         return Data; 
    } 

    const Ajax =new new Vue ({ 
        Methods: { 
　　　　　　　// Interface 1, to accept the url parameter, 
            GET (url) { 
                const XHR = createXhr (); 
                const Data = createData (); 
                xhr.open ( 'the GET', url + + Data '?' , to true ); 
                xhr.send ( null ); 
            }, 
　　　　　　　　// 2 the interface, accepts the url parameter 
            POST (url) { 
                const XHR = createXhr (); 
                const Data = createData (); 
                xhr.post ( 'the POST', url, to true );
                xhr.setRequestHeader(
                    'Content-Type',
                    'application/x-www-form-rulencoded'
                );
                xhr.send(data);
            }
        }
    });

    Vue.prototype.$ajax = ajax;

};

export default install;