Reduce duplicate code to halve large package sizes

[mhart]

Is your feature request related to a problem? Please describe.

Related to #1536 – each module is twice the size than it needs to be because it bundles near-identical cjs and es implementations.

If I do a basic install of 3 clients, pretty typical for a small Lambda function:

npm install @aws-sdk/client-s3 @aws-sdk/client-dynamodb @aws-sdk/client-ssm

It installs 145 packages and the node_modules directory is 36MB – so more than 10MB worth of deps for each client. Add a few more clients and you already have a pretty chunky Lambda function. This is getting close to the same size as the entire aws-sdk v2, with far fewer clients.

Looking into why it's so large, it seems that each module has a cjs and an es directory – presumably to cover both CommonJS and ESM modules in the one package. Each of these is quite large (eg, 3.4MB each for ssm) and includes a lot of duplicated code (eg a 1MB Aws_json1_1.js file)

Describe the solution you'd like

It would be great if the packages should be spilt into CJS and ESM modules. ESM support is native to Node.js from v12 onwards – so when v10 becomes EOL, this project could just stop adding features to the CJS modules without needing to bump to a new major version. People bundling their Lambdas using a bundler will likely be using the ESM versions too.

If that's too much of a burden, then it would be great to share configuration (eg JSON files) between implementations – it seems overkill to have completely separate implementations of purely configuration data – especially if this makes up the bulk of the size.

Describe alternatives you've considered

Another alternative is to remove Node.js v10 support altogether and only support ESM modules.

[trivikr]

The AWS SDK for JavaScript team has reduced install size by ~35%
Tweet https://twitter.com/trivikram/status/1446596564969930753

I'm closing this feature request over specific one suggesting splitting CJS and ES versions in #2889

[github-actions]

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