//仅供参考 xhr
function ajax(type ,url , data , successCallBack , errorCallBack){
 let xhr = new XMLHttpRequest();
 xhr.onload = ()=>{
 if(xhr.status === 200){
  return successCallBack(xhr.response||xhr.responseText);
 }
 return errorCallBack('请求失败');
 }
 xhr.onerror = ()=>{
 return errorCallBack('出错了');
 }
 xhr.open(type,url);
 xhr.send(data ? data:null);
}

ajax('get','/test/getUserList' , undefined , function(result){
 console.log('成功了。', result);
} ,function(error){
 console.log(error);
});

//仅供参考 xhr.abort
function ajax(type ,url , data , successCallBack , errorCallBack){
 let xhr = new XMLHttpRequest();
 xhr.onload = ()=>{
 if(xhr.status === 200){
  return successCallBack(xhr.response||xhr.responseText);
 }
 return errorCallBack('请求失败');
 }
 xhr.onerror = ()=>{
 return errorCallBack('出错了');
 }
 xhr.open(type,url);
 xhr.send(data ? data:null);
 return xhr;//返回XMLHttpRequest实例对象
}

let xhr = ajax('get','/test/getUserList' , undefined , function(result){
 console.log('成功了。', result);
} ,function(error){
 console.log(error);
});
//abort
xhr.abort();

//仅供参考 promise
function ajax(type ,url , data ){
 let xhr = new XMLHttpRequest();
 let promise = new Promise(function(resolve , reject){
 xhr.onload = ()=>{
  if(xhr.status === 200){
  return resolve(xhr.response||xhr.responseText);
  }
  return reject('请求失败');
 }
 xhr.onerror = ()=>{
  return reject('出错了');
 }
 xhr.open(type,url);
 xhr.send(data ? data:null);
 });
 return promise;//返回Promise实例对象
}

let promise = ajax('get','/test/getUserList');
promise.then((result)=>{
 console.log('成功了。', result);
},(error)=>{
 console.log(error);
})

let map = [];//用于保存promise和xhr之间的映射关系
//仅供参考 promise abort
function ajax(type ,url , data ){
 let xhr = new XMLHttpRequest();
 let promise = new Promise(function(resolve , reject){
 xhr.onload = ()=>{
  if(xhr.status === 200){
  return resolve(xhr.response||xhr.responseText);
  }
  return reject('请求失败');
 }
 xhr.onerror = ()=>{
  return reject('出错了');
 }
 xhr.open(type,url);
 xhr.send(data ? data:null);
 });
 map.push({promise:promise,request:xhr});//创建promise和xhr之间的映射关系，保存到全局的一个数组中。
 return promise;//返回Promise实例对象
}
//abort 请求
function abort(promise){
 for(let i = 0 ; i < map.length ; i++ ){
 if ( map[i].promise === promise ){
  map[i].request.abort();
 }
 }
}

let promise = ajax('get','/test/getUserList');
promise.then((result)=>{
 console.log('成功了。', result);
},(error)=>{
 console.log(error);
})
abort(promise);

let index = 0;
//仅供参考 jsonp
function jsonp(url,jsonp,successCallback , errorCallback){
 let script = document.createElement('script');
 let result ;
 script.onload = function(){
 successCallback(result);
 }
 script.onerror = function(){
 errorCallback('出错了');
 }
 let callBackName = 'jsonpCallback'+index++;
 script.src=url+(url.indexOf('?') >=0 ? '&':'?')+jsonp+'='+callBackName;
 window[callBackName]=function(){//拿给后端进行输出执行的。
 result = Array.prototype.slice.call(arguments);
 }
 document.head.append(script);
}

let query = ctx.request.query;
let jsonp = query.jsonp;//与后端协商的回调参数
ctx.body = jsonp+'({code:0,msg:"success"})';

<script >
 //只有这一行是服务器返回的，
 //script标签是document.head.append(script)时候加的
 jsonpCallback0({code:0,msg:"success"});
</script>

//[trigger 触发事件]
function trigger(element,event){
 if( !isString(event) ) {
 return;
 }
 if ( element.dispatchEvent ){
 let evt = document.createEvent('Events');// initEvent接受3个参数
 evt.initEvent(event, true, true);
 element.dispatchEvent(evt);
 }else if ( element.fireEvent ){ //IE
 element.fireEvent('on'+event);
 }else{
 element['on'+event]();
 }
}
let index = 0;
//仅供参考 jsonp.abort
function jsonp(url,jsonp,successCallback , errorCallback){
 let script = document.createElement('script');
 let result ;
 script.onload = function(){
 successCallback(result);
 }
 script.onerror = function(){
 errorCallback('出错了');
 }
 let callBackName = 'jsonpCallback'+index++;
 script.src=url+(url.indexOf('?') >=0 ? '&':'?')+jsonp+'='+callBackName;
 window[callBackName]=function(){//拿给后端进行输出执行的。
 result = Array.prototype.slice.call(arguments);
 }
 script.abort = ()=>{
 return trigger(script,'error');
 };
 document.head.append(script);
 return script;
}

let index = 0;
//仅供参考 jsonp.abort
function jsonp(url,query,jsonp){
 let script = document.createElement('script');
 let result ;
 let promise = new Promise(function(resolve,reject){
 script.onload = function(){
  return resolve(result);
 }
 script.onerror = function(){
  return reject('出错了');
 }
 let callBackName = 'jsonpCallback'+index++;
 script.src=url+(url.indexOf('?') >=0 ? '&':'?')+jsonp+'='+callBackName;
 window[callBackName]=function(){//拿给后端进行输出执行的。
  result = Array.prototype.slice.call(arguments);
 }
 document.head.append(script);
 });
 script.abort = ()=>{
 return trigger(script,'error');
 };
 map.push({promise:promise,request:script});//创建promise和script之间的映射关系，保存到全局的一个数组中。
 return promise;
}

let promise = jsonp('/test/getUserList','jsonp');
promise.then((result)=>{
 console.log('成功了。', result);
},(error)=>{
 console.log(error);
})
abort(promise);