@aws-sdk/client-s3 TypeError: A dynamic import callback was invoked without --experimental-vm-modules in jest

[H1Gdev]

Checkboxes for prior research

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

Describe the bug

When using the latest @aws-sdk/client-s3 with jest, the following error occurs.

    TypeError: A dynamic import callback was invoked without --experimental-vm-modules

    >  97 |         const s3Response = await s3.send(getObjectCommand);
          |                            ^

      at node_modules/@aws-sdk/credential-provider-node/dist-cjs/index.js:63:25
      at node_modules/@smithy/property-provider/dist-cjs/index.js:50:39
      at coalesceProvider (node_modules/@smithy/property-provider/dist-cjs/index.js:76:24)
      at node_modules/@smithy/property-provider/dist-cjs/index.js:95:24
      at node_modules/@smithy/core/dist-cjs/index.js:62:23
      at node_modules/@aws-sdk/middleware-sdk-s3/dist-cjs/index.js:90:20
      at node_modules/@aws-sdk/middleware-logger/dist-cjs/index.js:33:22

Regression Issue

• Select this option if this issue appears to be a regression.

SDK version number

@aws-sdk/client-s3@3.906.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

Node.js 22

Reproduction Steps

          const s3 = tracer.captureAWSv3Client(new S3({}));
          const putObjectCommand = new PutObjectCommand({
            Bucket: url.hostname,
            Key: url.pathname.substring(1),
            Body: await fs.readFile(tmpFilePath),
          });
          const s3Response = await s3.send(putObjectCommand);

Observed Behavior

TypeError occurs...

Expected Behavior

No errors should occur.

Possible Solution

No response

Additional Information/Context

No response

[aBurmeseDev]

Hi @H1Gdev - thanks for stopping by. This sounds like a testing error by Jest, rather than SDK issue.

Per this comment, you may need to explicitly enable the --experimental-vm-modules flag when running Jest. This flag tells Node to enable the experimental VM modules feature which is required for dynamic imports and other ESM functionalities within Jest's test runner.

Hope that helps!

[H1Gdev]

@aBurmeseDev

Thanks for your reply.
This error did not occur until at least 3.312.0.
Do you know which version this error started occurring ?

[rbnayax]

This comes from your code, not Jest. We should not turn on this experimental flag just for test, as this code will fail in produciton as well. Please have a look into this as this is a breaking change.
Thatnks for the help :-)

[rbnayax]

I investigated some more. In production, this will not fail. This is indeed an issue with Jest and esm syntax support. This issue was introduced once you started using import statements in the cjs code. Sadly, the only solution is to either revert that or enable the experimental flag.

[chrisjyoon]

It seems this has started from [3.906.0](https://github.com/aws/aws-sdk-js-v3/compare/v3.905.0...v3.906.0) (2025-10-08)

[TomiTakussaari]

I guess this MR caused this: #7406

By default, Rollup seems to keep dynamic imports: https://rollupjs.org/configuration-options/#output-dynamicimportincjs, while previous build system (esbuild) explicitly set dynamic imports support to false: https://github.com/aws/aws-sdk-js-v3/pull/7406/files#diff-806b212a2cb99c357b9e31ec0d79783c34663053f93d321606c9003a94b2c4d8L171, which presumably caused it to rewrite those using require.

Unless this change was really wanted (I hope not), perhaps dynamicImportInCjs=false could be added to rollup output options?

[karoly-kemeny]

We have this issue here as well. I understand that the root cause might be in jest, but breaking compatibility with the most used test runner in the industry is unfortunate. Could you pretty please allocate some capacity to make it properly compatible?

It is not that it is a free OSS product after all, we pay for this through our AWS bills.