@babel/plugin-transform-block-scoped-functions

What is @babel/plugin-transform-block-scoped-functions?

The @babel/plugin-transform-block-scoped-functions npm package is designed to ensure that functions defined within blocks (such as if statements or for loops) are properly scoped to those blocks in environments that may not support this feature natively. This is particularly useful for ensuring compatibility with older browsers or JavaScript environments that do not fully implement ES6 scoping rules.

What are @babel/plugin-transform-block-scoped-functions's main functionalities?

Function Scoping

This feature ensures that functions defined within a block are scoped to that block. This is important for compatibility with ES6, where functions are block-scoped, unlike in ES5 where they are function-scoped. The plugin transforms the code to work correctly in environments that do not support block scoping natively.

"use strict";\n\nif (true) {\n  function foo() { return 1; }\n}\n\nfoo(); // Throws ReferenceError in ES6, transformed code works by scoping function within the block

Other packages similar to @babel/plugin-transform-block-scoped-functions

@babel/plugin-transform-block-scoping

Similar to @babel/plugin-transform-block-scoped-functions, this package transforms let and const declarations to be properly scoped to blocks, ensuring compatibility with older environments. While @babel/plugin-transform-block-scoped-functions focuses specifically on function declarations, @babel/plugin-transform-block-scoping handles all block-scoped declarations.

@babel/preset-env

While not a direct equivalent, @babel/preset-env includes @babel/plugin-transform-block-scoped-functions as part of its comprehensive transformation of ES6+ code to be compatible with a target environment. It provides a broader range of transformations, including block-scoped functions, making it a more versatile choice for projects needing wide-ranging compatibility.

README

@babel/plugin-transform-block-scoped-functions

Babel plugin to ensure function declarations at the block level are block scoped

See our website @babel/plugin-transform-block-scoped-functions for more information.

Install

Using npm:

npm install --save-dev @babel/plugin-transform-block-scoped-functions

or using yarn:

yarn add @babel/plugin-transform-block-scoped-functions --dev

Changelog

v7.26.5 (2025-01-10)

:eyeglasses: Spec Compliance

• babel-parser
  • #17011 Allow the dynamic import.defer() form of import defer (@babel-bot)

:bug: Bug Fix

• babel-plugin-transform-block-scoped-functions
  • #17024 chore: Avoid calling isInStrictMode in Babel 7 (@liuxingbaoyu)
• babel-plugin-transform-typescript
  • #17026 fix: Correctly generate exported const enums in namespace (@liuxingbaoyu)
• babel-parser
  • #17045 [estree] Unify method type parameters handling (@JLHwung)
  • #17013 fix: Correctly set position for @(a.b)() (@liuxingbaoyu)
  • #16996 [estree] Adjust the start loc of class methods with type params (@nicolo-ribaudo)
• babel-generator, babel-parser, babel-plugin-transform-flow-strip-types, babel-types
  • #17028 Support flow jsx opening element type arguments (@JLHwung)
• babel-compat-data, babel-preset-env
  • #17031 fix: More accurate transform-typeof-symbol compat data (@liuxingbaoyu)
• babel-generator, babel-parser, babel-types
  • #17019 Fix incomplete visitor keys (@JLHwung)

:microscope: Output optimization

• babel-plugin-transform-nullish-coalescing-operator
  • #16612 Improve nullish coalescing operator output (@liuxingbaoyu)