The createBucket method is mutating the object passed as parameter

[eaviles]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone though Developer Guide and API reference
• I've checked AWS Forums and StackOverflow for answers
• I've searched for previous similar issues and didn't find any solution

Describe the bug
The createBucket method in AWS.S3 is mutating the object passed as parameter.

Is the issue in the browser/Node.js?
Node.js

If on Node.js, are you running this on AWS Lambda?
No

Details of the browser/Node.js version
v12.13.0

SDK version number
v2.585.0

To Reproduce (observed behavior)

const params = { Bucket: 'sample' };
await client.createBucket(params).promise();

After running the above core, the value of params is now:

{
  Bucket: 'sample',
  CreateBucketConfiguration: { LocationConstraint: 'us-east-1' }
}

Which causes problems if someone is reusing the same object in a different call, for example:

await client.waitFor('bucketExists', params).promise();
// which throws: [UnexpectedParameter] Unexpected key 'CreateBucketConfiguration' found in params

Expected behavior
After calling createBucket, the original object used as parameter shouldn't be mutated.

Workaround
Freezing the object before passing it as parameter seems to stop this behavior.

const params = Object.freeze({ Bucket: 'sample' });
await client.createBucket(params).promise();
await client.waitFor('bucketExists', params).promise();

As modules don't run in strict mode by default, the attempt to change the original object won't throw an exception and will just be ignored.

[ajredniwja]

Hey @eaviles, thank-you for reaching out to us with your issue.

I was not able to reproduce behavior can you please share how you are providing the region for your use case?

[lock]

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