不跨域或者可以跨域的話
function getMime(dist) {

            return new Promise(function(resolve,reject) {
                var xhr = new XMLHttpRequest();
                xhr.open('GET', dist);
                xhr.responseType = 'blob';
                xhr.onreadystatechange = function() {
                    if(xhr.readyState == 4) {
                        if((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304) {
                            resolve(xhr.response.type);
                        }else{
                            reject();
                        }
                    }
                }
                xhr.send();
            })
        }
        getMime().then(function(type){
            console.log(type)
        },function(){
            console.log('rejct')
        });