Similarly, Cloud Functions can also be triggered by changes in Cloud Storage buckets:

1. Write the Cloud Function and save it as index.js:

/**
 * Background Cloud Function to be triggered by Cloud Storage..
 */
exports.helloGCS = function (event, callback) 
{
 const file = event.data;

 if (file.resourceState === 'not_exists') 
{
 console.log(`File ${file.name} deleted.`);
 } 
else if (file.metageneration === '1') 
{
 // metageneration attribute is updated on metadata changes.
 // on create value is 1
 console.log(`File ${file.name} uploaded.`);
 }
 else 

{
 console.log(`File ${file.name} metadata updated.`);
 }

 callback();
};

2. Deploy the Cloud Function:

gcloud beta functions deploy helloGCS --trigger-bucket <BUCKET_NAME>  

3. Trigger (invoke) the Cloud Function
4. As before, we can invoke this function either by uploading a file (say test.txt) to the bucket, or through an equivalent direct invocation:

gcloud beta functions call helloGCS --data '{"name":"test.txt"}'

Once invoked, the logs should contain the log entry stating that test.txt file was uploaded to the GCS bucket.