XmlHttpRequest请求文件

function download(id) {
    let url = 'http://localhost:12879/Resource/ResourceDnld?id=' + id;
    let xhr=new XMLHttpRequest();
    xhr.open('post',url,true);
    xhr.responseType='blob';
    xhr.onload=function (res) {
        let filename="测试.json";
        if (this.status==200){
            let type=xhr.getResponseHeader('Content-Type');
            let blob=new Blob([this.response],{type:type});
            if (typeof window.navigator.msSaveBlob !=='undefined'){
                window.navigator.msSaveBlob(blob,filename);
            }
            else {
                let URL=window.URL || window.webkitURL;
                let  objectUrl = URL.createObjectURL(blob);
                if (filename){
                    let a=document.createElement('a');
                    if (typeof  a.download=='undefined'){
                        window.location=objectUrl;
                    }else {
                        a.href = objectUrl;
                        a.download = filename;
                        document.body.appendChild(a);
                        a.click();
                        a.remove()
                    }
                }else {
                    window.location=objectUrl;
                }
            }
            }
        }
    xhr.send();
}