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schangxiang@126.com

2025-09-19 18966e02fb573c7e2bb0c6426ed792b38b910940

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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.