@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

v7.27.3 (2025-05-27)

:bug: Bug Fix

• babel-generator
  • #17324 Improve multiline comments handling in yield/await expression (@JLHwung)
• babel-helpers, babel-plugin-transform-async-generator-functions, babel-plugin-transform-regenerator, babel-preset-env, babel-runtime-corejs3
  • #17328 Correctly set .displayName on GeneratorFunction (@nicolo-ribaudo)
• babel-plugin-proposal-explicit-resource-management
  • #17319 fix: handle shadowed binding in for using of body (@JLHwung)
  • #17317 fix: support named evaluation for using declaration (@JLHwung)
• babel-plugin-proposal-decorators, babel-types
  • #17321 fix(converter): Remove abstract modifiers in class declaration to expression conversion (@magic-akari)
• babel-helper-module-transforms, babel-plugin-proposal-explicit-resource-management, babel-plugin-transform-modules-amd, babel-plugin-transform-modules-commonjs, babel-plugin-transform-modules-umd
  • #17257 Preserve class id when transforming using declarations with exported class (@JLHwung)
• babel-parser
  • #17312 fix(parser): properly handle optional markers in generator class methods (@magic-akari)
  • #17307 fix(parser): Terminate modifier parsing at newline (@magic-akari)
• babel-generator, babel-parser
  • #17308 Improve import phase parsing (@JLHwung)