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# babel-plugin-transform-es2015-block-scoping
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> Compile ES2015 block scoping (const and let) to ES5
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## Installation
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```sh
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npm install --save-dev babel-plugin-transform-es2015-block-scoping
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```
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## Usage
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### Via `.babelrc` (Recommended)
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**.babelrc**
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Without options:
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```json
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{
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"plugins": ["transform-es2015-block-scoping"]
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}
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```
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With options:
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```json
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{
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"plugins": [
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["transform-es2015-block-scoping", {
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"throwIfClosureRequired": true
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}]
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]
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}
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```
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### Via CLI
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```sh
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babel --plugins transform-es2015-block-scoping script.js
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```
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### Via Node API
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```javascript
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require("babel-core").transform("code", {
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plugins: ["transform-es2015-block-scoping"]
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});
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```
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## Options `throwIfClosureRequired`
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In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:
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```javascript
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for (let i = 0; i < 5; i++) {
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setTimeout(() => console.log(i), 1);
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}
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```
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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.
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