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# babel-plugin-check-es2015-constants
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Validate ES2015 constants (prevents reassignment of const variables).
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## Example
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**In**
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```js
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const a = 1;
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a = 2;
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```
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**Out**
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```bash
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repl: "a" is read-only
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1 | const a = 1;
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> 2 | a = 2;
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| ^
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```
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[Try in REPL](http://babeljs.io/repl/#?babili=false&evaluate=true&lineWrap=false&presets=es2015&experimental=false&loose=false&spec=false&code=const%20a%20%3D%201%3B%0Aa%20%3D%202%3B&playground=true)
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## Installation
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```sh
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npm install --save-dev babel-plugin-check-es2015-constants
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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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```json
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{
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"plugins": ["check-es2015-constants"]
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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 check-es2015-constants 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: ["check-es2015-constants"]
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});
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```
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## Note
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This check will only validate consts. If you need it to compile down to `var` then you must also install and enable [`transform-es2015-block-scoping`](http://babeljs.io/docs/plugins/transform-es2015-block-scoping/).
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