@babel/helper-annotate-as-pure

What is @babel/helper-annotate-as-pure?

The @babel/helper-annotate-as-pure npm package is a utility within the Babel ecosystem designed to annotate call expressions with a /*#__PURE__*/ comment. This comment hints to JavaScript bundlers and minifiers, such as Terser, that the function call is pure. A pure function call's result can be safely removed if its result is not used, enabling more efficient final bundles by removing unused code.

What are @babel/helper-annotate-as-pure's main functionalities?

Annotating a call expression as pure

This feature allows developers to mark specific call expressions as pure, enabling potential removal during the minification process if the result of the call is unused. This is particularly useful for library authors who want to ensure their library's unused parts can be tree-shaken in consumer applications.

import * as t from '@babel/types';
import annotateAsPure from '@babel/helper-annotate-as-pure';

const callExpression = t.callExpression(t.identifier('myFunction'), []);
annotateAsPure(callExpression);
// The callExpression node is now annotated with a /*#__PURE__*/ comment.

Other packages similar to @babel/helper-annotate-as-pure

babel-plugin-annotate-pure-calls

Similar to @babel/helper-annotate-as-pure, this package provides a Babel plugin to automatically annotate call expressions and new expressions with /*#__PURE__*/ comments. The key difference is that it operates at the plugin level, automatically applying the annotations across your codebase, rather than requiring manual annotation of each call.

uglifyjs-webpack-plugin

While not a direct alternative, uglifyjs-webpack-plugin interfaces with UglifyJS to minify JavaScript bundles in Webpack projects. It can take advantage of the pure annotations added by @babel/helper-annotate-as-pure to perform tree shaking and dead code elimination, showcasing how such annotations can be utilized in the minification process.

README

@babel/helper-annotate-as-pure

Helper function to annotate paths and nodes with #PURE comment

See our website @babel/helper-annotate-as-pure for more information.

Install

Using npm:

npm install --save @babel/helper-annotate-as-pure

or using yarn:

yarn add @babel/helper-annotate-as-pure

Changelog

v7.25.9 (2024-10-22)

:bug: Bug Fix

• babel-parser, babel-template, babel-types
  • #16905 fix: Keep type annotations in syntacticPlaceholders mode (@liuxingbaoyu)
• babel-helper-compilation-targets, babel-preset-env
  • #16907 fix: support BROWSERSLIST{,_CONFIG} env (@JLHwung)
• Other
  • #16884 Analyze ClassAccessorProperty to prevent the no-undef rule (@victorenator)

:house: Internal

• babel-helper-transform-fixture-test-runner
  • #16914 remove test options flaky (@JLHwung)

:running_woman: Performance

• babel-parser, babel-types
  • #16918 perf: Make VISITOR_KEYS etc. faster to access (@liuxingbaoyu)