promise封装ajax

function getURL(URL){

    return new Promise((resolve,reject)=>{

        var req=newXMLHttpRequest();

        req.open('GET',URL,true);

        req.onload=function(){

            if(req.status===200){resolve(req.responseText);}

            else{reject(newError(req.statusText));}

        };

        req.onerror=function(){reject(newError(req.statusText));};

        req.send();

    });

}

// 运行示例

var URL="http://httpbin.org/get";

getURL(URL)

.then(function onFulfilled(value){console.log(value);})

.catch(function onRejected(error){console.error(error);});