How to update a variable NodeJs - node.js

Question

I am trying to update "documentCopyId" variable, but print undefined
function listFiles(auth) {
const drive = google.drive({ version: 'v3', auth });
const apiKey = 'xxxxx';
const paragraph = "Hello World";
let documentCopyId;
var copyTitle = "Copy Title";
let request = {
name: copyTitle,
};
drive.files.copy({
fileId: 'xxxx',
resource: request,
}, (err, driveResponse) => {
console.log('document from drive copy ' + driveResponse.data.id) //Print id
documentCopyId = driveResponse.data.id;
});
console.log('document from listFiles '+ documentCopyId); // print undefined
}
complete Log:
document from listFiles undefined
document from drive copy 1IjXkk5QgTNVT85xxxxxx

Answer 1

It is because the code
console.log('document from listFiles '+ documentCopyId); // print undefined
doesn't wait until this code completing
drive.files.copy({
fileId: 'xxxx',
resource: request,
}, (err, driveResponse) => {
console.log('document from drive copy ' + driveResponse.data.id) //Print id
documentCopyId = driveResponse.data.id;
});
which means that
console.log('document from listFiles '+ documentCopyId)
executing before
documentCopyId = driveResponse.data.id;
And in that case, documentCopyId is undefined.
As a solution, you can to promisify driver.files.copy part, and resolve the needed value. Or do need manipulations in a callback of drive.files.copy.
For example, you can do something like this
const listFiles = async (auth) => {
let documentCopyId;
const driveResponse = await copyPromise('Copy Title');
documentCopyId = driveResponse.data.id;
console.log('document from listFiles ' + documentCopyId);
};
const copyPromise = (name) => {
return new Promise((resolve, reject) => {
try {
const drive = google.drive({ version: 'v3', auth });
const apiKey = 'xxxxx';
const paragraph = 'Hello World';
let request = {
name
};
drive.files.copy(
{
fileId: 'xxxx',
resource: request,
},
(err, driveResponse) => {
if (err) throw new Error(err);
console.log('document from drive copy ' + driveResponse.data.id);
resolve(driveResponse);
}
);
} catch (error) {
console.log('Error in copyPromise:', error);
reject(error);
}
});
};