fetch请求实现文件下载

function getAttachment(url,fileName): void {
    let init = {
        headers: {'Accept':'application/octet-stream'}
    }

    fetch(url, init).then(res => {
        try {
            res.blob().then(blob => {
                var filename=`${fileName}`
                if (window.navigator.msSaveOrOpenBlob) {
                    navigator.msSaveBlob(blob, filename);  //兼容ie10
                } else {
                    var a = document.createElement('a');
                    document.body.appendChild(a) //兼容火狐，将a标签添加到body当中
                    var url = window.URL.createObjectURL(blob);   // 获取 blob 本地文件连接 (blob 为纯二进制对象，不能够直接保存到磁盘上)
                    a.href = url;
                    a.download = filename;
                    a.target='_blank'  // a标签增加target属性
                    a.click();
                    a.remove()  //移除a标签
                    window.URL.revokeObjectURL(url);
                }
            })
        }catch(e){

        }

    })
}