php查询数据，输出为base64格式的字符串作为url和文件名，前端直接js下载。

lrEle.postAndDone({
    url: '/addons/device/download/exportQxtExcel/deviceId/'+ deviceId,
    postData: datas,
    successKey: 'code',
    successVal: '1',
    successFunc: function (res) {
        lrBox.noLoading();
        let xhr = new XMLHttpRequest();
        xhr.open('GET', res.data.file, true);
        xhr.setRequestHeader("Content-Type", 'application/json;charset=utf-8');
        xhr.responseType = 'blob';
        xhr.onload = function (e) {
            if (this.status == 200) {
                let blob = this.response;
                let a = document.createElement('a');
                let url = window.URL.createObjectURL(blob);
                a.href = url;
                a.download = res.data.filename;
                a.click();
                window.URL.revokeObjectURL(url);
            }
        };
        xhr.send();
    },
    errFunc: function (res) {
        lrBox.noLoading();
        lrBox.msgTisf(res.msg);
    }
});