js通过blob来下载文件，兼容IE

var fileName = "test.txt";
var str = "12345";
var blob = new Blob([str]);
//IE浏览器使用msSaveBlob
if (window.navigator.msSaveBlob){
    window.navigator.msSaveBlob(blob, fileName);
}else{
    var aLink = document.createElement('a');
    aLink.download = fileName;
    aLink.href = URL.createObjectURL(blob);
    aLink.click();
}

支持后台回传buffer到前端组成文件

//buf buffer
var arrayBuffer=new ArrayBuffer(buf.length);
var bufView = new Uint8Array(arrayBuffer);
for(var i=0;i<buf.length;i++){
    bufView[i]=buf[i];
}
var blob = new Blob([arrayBuffer], {type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;charset=utf-8'})

也支持xml或者json