The @babel/plugin-transform-block-scoping npm package is a Babel plugin that transforms JavaScript code to convert block scoping (let and const) to function scoping (var) where necessary. This is particularly useful for ensuring compatibility with older environments that do not support ES6 block-scoped variables.

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

Transform let and const to var

This feature transforms block-scoped variables (let and const) into function-scoped variables (var) to ensure compatibility with older JavaScript engines.

if (true) {
  let x = 'hello';
}
// Transformed to:
if (true) {
  var x = 'hello';
}

Block scoping for loops

This feature correctly scopes the loop variable within closures, preventing common errors when using setTimeout or similar asynchronous functions within loops.

for (let i = 0; i < 3; i++) {
  setTimeout(function() { console.log(i); }, 0);
}
// Transformed to:
for (var i = 0; i < 3; i++) {
  (function(i) {
    setTimeout(function() { console.log(i); }, 0);
  })(i);
}

Other packages similar to @babel/plugin-transform-block-scoping

Changelog

Source

v7.20.5 (2022-11-28)

:eyeglasses: Spec Compliance

babel-helpers, babel-plugin-transform-destructuring, babel-plugin-transform-modules-commonjs, babel-preset-env, babel-runtime-corejs2, babel-runtime-corejs3, babel-runtime, babel-traverse
- #15183 Improve array destructuring spec compliance (@SuperSodaSea)
babel-cli, babel-helpers, babel-plugin-proposal-class-properties, babel-plugin-proposal-class-static-block, babel-plugin-transform-classes, babel-plugin-transform-runtime, babel-preset-env
- #15182 fix: apply toPropertyKey when defining class members (@JLHwung)
babel-helper-create-class-features-plugin, babel-helpers, babel-plugin-proposal-decorators, babel-plugin-proposal-private-property-in-object, babel-preset-env, babel-runtime-corejs2, babel-runtime-corejs3, babel-runtime
- #15133 fix: validate rhs of in when transpiling #p in C (@JLHwung)

:bug: Bug Fix

babel-parser
- #15225 Parse using[foo] as computed member expression (@JLHwung)
- #15207 Export ParseResult type (@davydof)
- #15198 fix: parse import module, ... (@JLHwung)
babel-helper-wrap-function, babel-preset-env, babel-traverse
- #15181 fix: Edge cases for async functions and noNewArrow assumption (@liuxingbaoyu)
babel-plugin-transform-arrow-functions, babel-plugin-transform-parameters, babel-traverse
- #15163 fix: Throw error when compiling super() in arrow functions with default / rest parameters (@SuperSodaSea)
babel-helpers, babel-node, babel-plugin-proposal-async-generator-functions, babel-plugin-transform-regenerator, babel-preset-env, babel-runtime-corejs2, babel-runtime-corejs3, babel-runtime
- #15194 fix: Bump regenerator and add tests (@SuperSodaSea)
babel-helper-create-regexp-features-plugin
- #15192 fix: Update regjsparser for @babel/standalone (@liuxingbaoyu)
babel-parser, babel-types
- #15109 fix: Babel 8 types (@liuxingbaoyu)
babel-generator
- #15143 Don't print inner comments as leading when wrapping in (``) (@nicolo-ribaudo)
babel-plugin-transform-block-scoping, babel-traverse
- #15167 Register switch's discriminant in the outer scope (@nicolo-ribaudo)

:nail_care: Polish

babel-generator
- #15173 Improve generator behavior when comments:false (@liuxingbaoyu)
babel-plugin-transform-block-scoping
- #15164 Only extract IDs for TDZ checks in assign when necessary (@nicolo-ribaudo)

:house: Internal

babel-core, babel-parser
- #15202 Bump typescript to 4.9.3 (@JLHwung)

Readme

Source