@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.

Examples

In

{
  function name (n) {
    return n;
  }
}

name("Steve");

Out

{
  let name = function (n) {
    return n;
  };
}
name("Steve");

Installation

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

Usage

Via .babelrc (Recommended)

.babelrc

{
  "plugins": ["@babel/plugin-transform-block-scoped-functions"]
}

Via CLI

babel --plugins @babel/plugin-transform-block-scoped-functions script.js

Via Node API

require("@babel/core").transform("code", {
  plugins: ["@babel/plugin-transform-block-scoped-functions"]
});