封装promise

const getJSON = function(url,type,data) {

const promise = new Promise(function(resolve, reject){

const handler = function() {

if (this.readyState !== 4) {

return;

};

if (this.status === 200) {

resolve(this.response);

} else {

reject(new Error(this.statusText));

}

};

const client = new XMLHttpRequest();

client.open(type, url);

client.onreadystatechange = handler;

client.responseType = "json";

if(type=='get'){

client.send();

}else {

client.setRequestHeader("Content-Type","application/json");//data只能是JSON字符串

client.send(JSON.stringify(data)) //post请求传入string

}

 

});

return promise;

};

 

 

 

调用案例

$(function() {

  $("button").click(function() {  

     getJSON('http://localhost:3000/info','get').then( res => {

    　　//success

   　　console.log('ok');

     }).catch( res=> {

          console.error('出错了', error);

    });

  });

//JQUERY 1.5.0返回的是xhr对象 高于1.5.0返回的deferred对象

})