node.js – 尝试将文件从aws s3下载到nodejs writeStream中

我试图从s3下载文件,并使用Nodejs中的writeStream直接放入文件系统中的文件.这是我的代码：

downloadFile = function(bucketName,filename,localFileName) {
    //Donwload the file
    var bucket = new AWs.S3({
        params: { Bucket: bucketName },signatureVersion: 'v4'
    });
    var file = require('fs').createWriteStream(localFileName);
    var request = bucket.getObject({ Key: filename });
    request.createReadStream().pipe(filE);
    request.send();
    return request.promise();
}

运行此函数我收到此错误：

Uncaught Error: write after end

怎么了？写入完成之前文件是否已关闭？为什么？

var s3 = new AWs.S3({
    accessKeyId: accessKeyId,secretAccessKey: secretAccessKey
}),file = fs.createWriteStream(localFileName);
s3
.getObject({
    Bucket: bucketName,Key: filename
})
.on('error',function (err) {
    console.log(err);
})
.on('httpData',function (chunk) {
    file.write(chunk);
})
.on('httpDone',function () {
    file.end();
})
.send();