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# babel-plugin-transform-es2015-block-scoping
> Compile ES2015 block scoping (const and let) to ES5
## Installation
```sh
npm install --save-dev babel-plugin-transform-es2015-block-scoping
```
## Usage
### Via `.babelrc` (Recommended)
**.babelrc**
Without options:
```json
{
"plugins": ["transform-es2015-block-scoping"]
}
```
With options:
```json
{
"plugins": [
["transform-es2015-block-scoping", {
"throwIfClosureRequired": true
}]
]
}
```
### Via CLI
```sh
babel --plugins transform-es2015-block-scoping script.js
```
### Via Node API
```javascript
require("babel-core").transform("code", {
plugins: ["transform-es2015-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:
```javascript
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.
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