Generating QR codes in serverless with aws-nodejs template - node.js

Question

I need to write a lambda function and send a number in the api request field to genrate the number of QR codes and store them in a S3 bucket.I am using the serverless framework with the aws-nodejs template.
To describe the task briefly lets say I get a number input in the api request PathParameters and based on these number I have to generate those number of QR's using the qr npm package and then store these generated qr's in the s3 bucket
this is what i have been able to do so far.
module.exports.CreateQR = (event,context) =>{
const numberOfQR = JSON.parse(event.pathParameters.number) ;
for(let i=0;i<numberOfQR;i++){
var d= new Date();
async function createQr(){
let unique, cipher, raw, qrbase64;
unique = randomize('0', 16);
cipher = key.encrypt(unique);
raw = { 'version': '1.0', data: cipher, type: 'EC_LOAD'}
// linkArray.forEach( async (element,index) =>{
let qrcode = await qr.toDataURL(JSON.stringify(raw));
console.log(qrcode);
// fs.writeFileSync('./qr.html', `<img src="${qrcode}">`)
const params = {
Bucket:BUCKET_NAME,
Key:`QR/${d}/img${i+1}.jpg`,
Body: qrcode
};
s3.upload(params , function(err,data){
if(err){
throw err
}
console.log(`File uploaded Successfully .${data.Location}`);
});
}
createQr();
}
};
I have been able to upload a given number of images to the bucket but the issue i am facing is the images are not going in the order.I think the problem is with the asynchronous code. Any idea how to solve this issue

Answer 1

that's because you're not awaiting the s3 to upload, but instead you have a callback.
you should use the .promise of s3 and then await it, so you'll wait the file to be uploaded before move to the next one
I changed the example of code
See docs:
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#upload-property
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3/ManagedUpload.html#promise-property
// see the async keyword before the lambda function
// we need it for use the await keyword and wait for a task to complete before continue
module.exports.CreateQR = async (event,context) =>{
const numberOfQR = JSON.parse(event.pathParameters.number) ;
// moved your function out of the loop
function createQr(){
// ...
// here we call .promise and return it so we get a Task back from s3
return s3.upload(params).promise();
}
for(let i=0;i<numberOfQR;i++){
// ....
// here we await for the task, so you will get the images being created and uploaded in order
await createQr();
}
};
hope it guide you towards a solution.