CODEWITHSUNDEEP
javascriptnode.js
Anshul Goyal
Anshul Goyal

Reputation: 139

Node.js promise chaining

I am new to Node.js and am able to run these commands one by one one using promises:

let promise1 = new Promise(function (resolve, reject) {
sftp.connect({
    host: host,
    username: user,
    privateKey: fs.readFileSync(pemfile)
}).then(() => {
    return sftp.get(remotePath, fs.createWriteStream(localPath));   //This writes from a remote file to a local file
}).then(() => {
    sftp.end();
    resolve();
})
    .catch(err => {
        console.error(err.message);
        reject(err);
    });
});

await promise1;

let promise2 = new Promise(function (resolve, reject) {
    fs.readFile(localPath, 'utf8', function (err, data) {
        if (err) {
            reject(err);
        }
        resolve(data);
    });
});

let data  = await promise2;

This works but I know this is not the best way to do this. Is there a better way to do this?

Upvotes: 2

Views: 106

Answers (1)

MHassan
MHassan

Reputation: 435

await can be used directly with methods that return promise like sftp.connect, sftp.get, sftp.end so you can use it directly and the function will wait until the step is completed. Only fs.readfile does not return a Promise but we can call fs.promises.readFile() that returns promise then we can use await.

The code can be simplified:

try {

    await sftp.connect({
        host: host,
        username: user,
        privateKey: fs.readFileSync(pemfile)

    }) 

    await sftp.get(remotePath, fs.createWriteStream(localPath));   
    await sftp.end();
    let fileData = await fs.promises.readFile(localPath, 'utf8');
    console.log(fileData);

} catch (error) {
    console.error(error.message);
}

The try-catch block has been added to capture errors from any action.

Upvotes: 5

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