Feature request: Add support for ES Modules with esbuild.

[santiperone]

Describe your idea/feature/enhancement

Currently, when trying to use ES modules features (as described in https://aws.amazon.com/es/blogs/compute/using-node-js-es-modules-and-top-level-await-in-aws-lambda/) together with esbuild, some errors are thrown because the default output format for esbuild is .cjs, which doesn't support those.

Proposal

Add some option to change the output format to .mjs (maybe it could even be the default value)

[mildaniel]

Hey @santiperone, thanks for reporting this. SAM-CLI should already be exposing the format property, though I see it missing from our documentation which we will fix.

Can you try using one of the supported esbuild formats as defined in their documentation and see if it works
https://esbuild.github.io/api/#format

[santiperone]

Hi @mildaniel Thanks fo your response. You're right, there's actually a "Format" property that allows to set the output format to "esm". However, the output file still has ".js" extension instead of ".mjs" which makes the lambda runtime treat it as commonJs and makes it impossible to run. Also, is there any way of setting some of the esbuild properties globally? It's kind of a pain having to set that up on every function.

[mildaniel]

Hey @santiperone. I moved the issue to the Lambda Builders repository. This is our build engine that handles the relevant logic. I also opened a pull request to add support for the --out-extension flag which will allow you to specify .mjs as the file extensions by adding this snippet to your template.

BuildMethod: esbuild
BuildProperties:
    OutExtension: 
     - .js=.mjs

As for your configuration concern, it's one we've heard before and are actively working on.

[mildaniel]

This has now been released in AWS-SAM-CLI version 1.72.0!