Transpiler and polyfill bloat

babel.config.json

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "usage",
        "corejs": "3.38.1"
      }
    ]
  ],
  "exclude": "**/core-js"
}

input.js

console.log([1, 2, 3].at(-1));

output.js

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polyfill_dependencies.txt

core-js/modules/es.array.at.js
core-js/internals/export.js
core-js/internals/to-object.js
core-js/internals/length-of-array-like.js
core-js/internals/to-integer-or-infinity.js
core-js/internals/add-to-unscopables.js
core-js/internals/global-this.js
core-js/internals/object-get-own-property-descriptor.js
core-js/internals/create-non-enumerable-property.js
core-js/internals/define-built-in.js
core-js/internals/define-global-property.js
core-js/internals/copy-constructor-properties.js
core-js/internals/is-forced.js
core-js/internals/require-object-coercible.js
core-js/internals/to-length.js
core-js/internals/math-trunc.js
core-js/internals/well-known-symbol.js
core-js/internals/object-create.js
core-js/internals/object-define-property.js
core-js/internals/descriptors.js
core-js/internals/object-property-is-enumerable.js
core-js/internals/create-property-descriptor.js
core-js/internals/function-call.js
core-js/internals/to-property-key.js
core-js/internals/to-indexed-object.js
core-js/internals/ie8-dom-define.js
core-js/internals/has-own-property.js
core-js/internals/is-callable.js
core-js/internals/make-built-in.js
core-js/internals/own-keys.js
core-js/internals/is-null-or-undefined.js
core-js/internals/fails.js
core-js/internals/symbol-constructor-detection.js
core-js/internals/use-symbol-as-uid.js
core-js/internals/shared.js
core-js/internals/uid.js
core-js/internals/an-object.js
core-js/internals/enum-bug-keys.js
core-js/internals/html.js
core-js/internals/hidden-keys.js
core-js/internals/object-define-properties.js
core-js/internals/document-create-element.js
core-js/internals/v8-prototype-define-bug.js
core-js/internals/shared-key.js
core-js/internals/to-primitive.js
core-js/internals/is-symbol.js
core-js/internals/indexed-object.js
core-js/internals/function-bind-native.js
core-js/internals/function-uncurry-this.js
core-js/internals/inspect-source.js
core-js/internals/internal-state.js
core-js/internals/get-built-in.js
core-js/internals/function-name.js
core-js/internals/object-get-own-property-names.js
core-js/internals/object-get-own-property-symbols.js
core-js/internals/environment-v8-version.js
core-js/internals/shared-store.js
core-js/internals/is-object.js
core-js/internals/object-keys.js
core-js/internals/ordinary-to-primitive.js
core-js/internals/get-method.js
core-js/internals/object-is-prototype-of.js
core-js/internals/classof-raw.js
core-js/internals/weak-map-basic-detection.js
core-js/internals/object-keys-internal.js
core-js/internals/is-pure.js
core-js/internals/environment-user-agent.js
core-js/internals/a-callable.js
core-js/internals/array-includes.js
core-js/internals/try-to-string.js
core-js/internals/to-absolute-index.js

I have no ideas how do you transpile it, but the most of those dependencies should not be added. At least, core-js/modules/es.array.at should be the only module from the /modules/ path.

https://bundlejs.com/?q=core-js%2Fmodules%2Fes.array.at.js&treeshake=%5B*%5D&text=%22console.log%28%5B1%2C+2%2C+3%5D.at%28-1%29%29%3B%22

the practice of excluding the node_modules directory from transpilation is not a good practice

It seems, this is your mistake. At least, core-js should be excluded from transpiling for avoiding circular dependencies. I'm not sure even that your bundle works at all.

I'm happy to update the example to better reflect typical configurations. The configuration I used relied on as many defaults as possible (for the reasons stated in my article). Here's what was in my babel.config.json file:

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "usage",
        "corejs": "3.38.1"
      }
    ]
  ]
}

That being said, I do want this example to be reflective of typical Babel and core-js usage, and I agree that typical usage does exclude node_modules, so I will update it.

It seems, this is your mistake. At least, core-js should be excluded from transpiling for avoiding circular dependencies.

I disagree with this. I don't think it should matter whether a developer excludes core-js dependencies, especially considering the default Babel behavior is to not to exclude any dependencies.

I haven't looked into why Babel is adding additional dependencies when processing core-js polyfills, but it seems problematic to me that Babel, while processing core-js dependencies, is identifying that it needs to add additional polyfills, given that core-js is entirely authored in ES5. Though I guess that is a Babel issue and not a core-js issue.

@zloirock I updated this gist and the article. The output is now 11,217 bytes minified and includes 71 dependencies.