@babel/plugin-transform-block-scoping

Compile ES2015 block scoping (const and let) to ES5

Examples

{
  let a = 3
}

let a = 3

Out

{
  var _a = 3;
}

var a = 3;

Installation

npm install --save-dev @babel/plugin-transform-block-scoping

Usage

Via `.babelrc` (Recommended)

.babelrc

Without options:

{
  "plugins": ["@babel/transform-block-scoping"]
}

With options:

{
  "plugins": [
    ["@babel/transform-block-scoping", {
      "throwIfClosureRequired": true
    }]
  ]
}

Via CLI

babel --plugins @babel/transform-block-scoping script.js

Via Node API

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

Options `throwIfClosureRequired`

In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:

for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 1);
}

In extremely performance-sensitive code, this can be undesirable. If "throwIfClosureRequired": true is set, Babel throws when transforming these patterns instead of automatically adding an additional function.

README.md