nodejs异步等待流程无法正常工作答案

【问题标题】：nodejs async await flow not working correctlynodejs异步等待流程无法正常工作
【发布时间】：2021-10-16 13:25:19
【问题描述】：

我想创建一个端点来下载视频并将此视频上传到 Youtube。

首先我从请求正文中获取视频网址。其次，我将此视频保存到临时文件夹。之后我将此视频上传到 YouTube 频道最后一步是删除临时视频。

所以我的代码是这样剪断的：

    const videoUrl = req.body.video_url;
    ....
    ....
    var download = async function (url: any, dest: any, cb: any) {
        var file = fs.createWriteStream(dest);
        var request = https.get(url, function (response: any) {
            response.pipe(file);
            file.on('finish', function () {
                file.close(cb);
            });
        }).on('error', function (err: any) {
            fs.unlink(dest);
            if (cb) cb(err.message);
        });
    };

    const video = await download(videoUrl, file, function () {
        console.log('Video Download Successfull');  ===============> 3rd console output
    });
    ....
    ....
    var readStream = await fs.createReadStream(file);
    readStream.on('error', function (err: any) {

    });

    var request: any = await Youtube.videos.insert({
        resource: {
            snippet: {
                title: title
                , description: description
            }
            , status: {
                privacyStatus: "private"
            }
        }
        , part: "snippet,status"
        , media: {
            body: readStream
        }
    }, (err: any, data: any) => {
        if (err) {
            console.log(err.response.data.error)
            res.status(500).json({
                status: "Fail",
                message: "Youtube Video Upload Failed"
            })
        }
        else {
            try {
                fs.unlinkSync(file)
                console.log("temp video file deleted from server"); ===============> 1st console output
            } catch (err) {
                console.log("temp video file not deleted")
                console.error(err)
            }
            res.status(200).json({
                status: "Success",
                message: "Youtube Video Upload Successfull"
            })
            console.log("Video upload to youtube Successfull."); ===============> 2nd console output
        }

    });

当我调用这个端点时，控制台输出如下：

temp video file deleted from server  
Video upload to youtube Successfull. 
Video Download Successfull

但是控制台输出应该是：

Video Download Successfull
Video upload to youtube Successfull.     
temp video file deleted from server

为什么我的流程不正确。我该如何解决这个问题？

【问题讨论】：

异步函数不应该接受回调参数，它应该返回一个承诺。否则await 将不起作用。

标签： javascript node.js typescript express async-await

【解决方案1】：

你必须使用 Promises，这里我使用了 Promises 下载视频功能。

const videoUrl = req.body.video_url;
....
....
var download = async function (url: any, dest: any, cb: any) {
    return new Promise((resolve, reject) => {
        try {
            var file = fs.createWriteStream(dest);
            var request = https.get(url, function (response: any) {
                response.pipe(file);
                file.on('finish', function () {
                    file.close(cb);
                    resolve(true)
                });
            }).on('error', function (err: any) {
                fs.unlink(dest);
                if (cb) cb(err.message);
                reject(false)
            });
        }catch (e) {
            reject(false)
        }
        })
};

const video = await download(videoUrl, file)
if (video){
    console.log('download success')
}
....
....
var readStream = await fs.createReadStream(file);
readStream.on('error', function (err: any) {

});

var request: any = await Youtube.videos.insert({
    resource: {
        snippet: {
            title: title
            , description: description
        }
        , status: {
            privacyStatus: "private"
        }
    }
    , part: "snippet,status"
    , media: {
        body: readStream
    }
}, (err: any, data: any) => {
    if (err) {
        console.log(err.response.data.error)
        res.status(500).json({
            status: "Fail",
            message: "Youtube Video Upload Failed"
        })
    }
    else {
        try {
            fs.unlinkSync(file)
            console.log("temp video file deleted from server"); ===============> 1st console output
        } catch (err) {
            console.log("temp video file not deleted")
            console.error(err)
        }
        res.status(200).json({
            status: "Success",
            message: "Youtube Video Upload Successfull"
        })
        console.log("Video upload to youtube Successfull."); ===============> 2nd console output
    }

});

【讨论】：