XHR post请求下载文件

var filename = 'test.xlsx';
var xhr = new XMLHttpRequest();
xhr.open('POST', downloadExcel, true);
xhr.setRequestHeader("Content-Type", "application/json");
xhr.responseType = 'blob';
xhr.onload = function(res) {
    if (this.status === 200) {
        var type = xhr.getResponseHeader('Content-Type');
        var blob = new Blob([this.response], {type: type});
        if (typeof window.navigator.msSaveBlob !== 'undefined') {
            /*
             * For IE
             * >=IE10
             */
            window.navigator.msSaveBlob(blob, filename);
        } else {
            /*
             * For Non-IE (chrome, firefox)
             */
            var URL = window.URL || window.webkitURL;
            var objectUrl = URL.createObjectURL(blob);
            if (filename) {
                var 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(JSON.stringify(list));