前端下载文件操作

```javascript

getExportList({ }) {

        this.exportFlag = true;

        this.exportTxt = '生成报表中···';

        this.exportPercent = 50;

        let xhr = new XMLHttpRequest();

        let that = this;

        const downloadUrl = '/deviceManager/device/report_export';

        xhr.onload = function (event) {

            if ((xhr.status >= 200 && xhr.status < 300) || xhr.status < 300) {

                let type = xhr.getResponseHeader('Content-Type');

                console.log(type);

                //二进制文件流

                if (type === 'application/octet-stream') {

                    let blob = new Blob([this.response])

                    var a = document.createElement('a');

                    a.style.display = 'none';

                    var url = window.URL.createObjectURL(blob);

                    var filename = decodeURIComponent(xhr.getResponseHeader('Content-Disposition')).split('=')[1];

                    a.href = url;

                    a.download = filename;

                    document.body.appendChild(a);

                    a.click();

                    window.URL.revokeObjectURL(url);

                    document.body.removeChild(a);

                    that.exportPercent = 100;

                    that.message.create('success', '报表已生成');

                    that.exportClass = true;

                    setTimeout(() => {

                        that.exportFlag = false;

                    }, 1000)

                } else {

                    that.message.create('error', this.response.msg || '报表导出失败');

                    setTimeout(() => {

                        that.exportFlag = false;

                    }, 1000)

                }

            } else {

                that.message.create('error', this.response.msg || '报表导出失败');

                setTimeout(() => {

                    that.exportFlag = false;

                }, 1000)

            }

        };

        xhr.onprogress = (event) => {

            var divStatus = document.getElementById('status');

            console.log(event);

            if (event.lengthComputable) {

                console.log(event);

            }

        };

        xhr.open('get', downloadUrl, true);

        xhr.responseType = 'blob';

        xhr.send(null);

    };

```

重点是 xhr.responseType = 'blob';  要设置为blob  封装 保存的文件通过blob解析就会有问题