ESBuild doesn't tree shake *Client imports

[trivikr]

Describe the bug

ESBuild doesn't tree shake *Client imports

This is probably an issue with esbuild or my configuration. I'm creating a bug report with minimal repro.

Your environment

SDK version number

@aws-sdk/[email protected]

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

Node.js

Details of the browser/Node.js/ReactNative version

$ node -v
v16.14.2

$ ./node_modules/.bin/esbuild --version
0.14.36

Steps to reproduce

// bare-bones-client.mjs
import { ACMClient, ListCertificatesCommand } from "@aws-sdk/client-acm";

export const listCertificates = () => {
  const client = new ACMClient({ region: "us-west-2" });
  return client.send(new ListCertificatesCommand({}));
};

// aggregated-client.mjs
import { ACM } from "@aws-sdk/client-acm";

export const listCertificates = () => {
  const client = new ACM({ region: "us-west-2" });
  return client.listCertificates({});
};

Observed behavior

$ ./node_modules/.bin/esbuild bare-bones-client.mjs --bundle --outfile=out.js --platform=node 
  out.js  750.0kb

$ ./node_modules/.bin/esbuild aggregated-client.mjs --bundle --outfile=out.js --platform=node 
  out.js  749.9kb

Expected behavior

I was expecting the bundle created from bare-bones-client.mjs to be much smaller.

[trivikr]

This is probably an issue with esbuild or some configuration, as it's present in @aws-sdk/[email protected] too.

$ ./node_modules/.bin/esbuild bare-bones-client.mjs --bundle --outfile=out.js --platform=node
  out.js  542.4kb

$ ./node_modules/.bin/esbuild aggregated-client.mjs --bundle --outfile=out.js --platform=node
  out.js  542.4kb

[trivikr]

Probably related evanw/esbuild#1420

[AllanZhengYP]

I don't see you supplied a tree-shake config, here is the esbuild config I used for our bundler test.

[trivikr]

From esbuild docs on tree shaking, it's enabled when bundling

By default, tree shaking is only enabled either when bundling is enabled or when the output format is set to iife, otherwise tree shaking is disabled.

I force-enabled tree-shaking by setting --tree-shaking=true, and verified that bundle size doesn't change:

$ ./node_modules/.bin/esbuild bare-bones-client.mjs --bundle --outfile=out.js --platform=node --tree-shaking=true
  out.js  750.0kb

$ ./node_modules/.bin/esbuild aggregated-client.mjs --bundle --outfile=out.js --platform=node --tree-shaking=true
  out.mjs  749.9kb 

[trivikr]

Prior issues related to bundling:

• Webpack 5 warning "Should not import named export from default-exporting module" #1504
• webpack doesn't reduce the size of bundle when commands are imported #1617

[trivikr]

Experimented with cjs code, but there's no difference:

// bare-bones-client.js
const { ACMClient, ListCertificatesCommand } = require("@aws-sdk/client-acm");

export const listCertificates = () => {
  const client = new ACMClient({ region: "us-west-2" });
  return client.send(new ListCertificatesCommand({}));
};

// aggregated-client.js
const { ACM } = require("@aws-sdk/client-acm");

export const listCertificates = () => {
  const client = new ACM({ region: "us-west-2" });
  return client.listCertificates({});
};

$ ./node_modules/.bin/esbuild bare-bones-client.js --bundle --outfile=out.js --platform=node 
  out.js  749.7kb

$ ./node_modules/.bin/esbuild aggregated-client.js --bundle --outfile=out.js --platform=node
  out.js  749.6kb

[trivikr]

This happens as esbuild can't tree shake commonjs modules

This means tree shaking will likely not happen for packages that provide both module and main since tree shaking works with ECMAScript modules but not with CommonJS modules.

The application can explicitly pass --main-fields=module,main to enable tree-shaking

$ ./node_modules/.bin/esbuild aggregated-client.mjs --bundle --outfile=out.js --platform=node --main-fields=module,main
  out.js  591.5kb

$ ./node_modules/.bin/esbuild bare-bones-client.mjs --bundle --outfile=out.js --platform=node --main-fields=module,main
  out.js  486.9kb

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