ajax封装

function ajax(method,url,data) {

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

        let xhr = null; 

        try {
            xhr = new XMLHttpRequest();
        }catch(e) {
            xhr = new ActiveXObject("Microsoft.XMLHTTP");
        }

        // get post 
        if(method === ‘get‘ && data) {
            url += ‘?‘ + data;
        }


        xhr.open(method,url,true);

        if(method === ‘get‘) {
            xhr.send();
        }else {
            xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");
            xhr.send(data);
        }


        xhr.onreadystatechange = function() {
            if(xhr.readyState == 4) {
                if(xhr.status == 200) {
                    resolve(xhr.responseText)
                }else {
                    reject(xhr.status)
                }
            }
        }
    })

}