Node.js esbuild support for --main-fields properties

[santiperone]

Describe your idea/feature/enhancement

When running the beta features for esbuild, I noticed large bundle sizes for functions using aws-sdk v3 packages.
After some further research, I found this thread: aws/aws-sdk-js-v3#3023 which points out to specifying --main-fields=module,main when bundling with the sdk to allow for better tree shaking. This made my bundle go from:

to:

Proposal

Add the ability to set this property in the template, to allow for lower sizes bundles. It could be added as an additional properti inside the "BuildProperties"

[jfuss]

@santiperone Thanks for the report. I connected with @mildaniel who is working on the ESBuild integration. I think this is an easy change for us to support.

[lucashuy]

Thanks for opening this suggestion! The MainFields property is now available in SAM CLI release 1.56.0 under the BuildProperties section. Please refer the documentation for more details: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-using-build-typescript.html