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# @babel/helpers
> Collection of helper functions used by Babel transforms.
## Install
```sh
npm install --save-dev @babel/helpers
```
## Usage
Direct:
```js
import * as helpers from '@babel/helpers';
import * as t from '@babel/types';
const typeofHelper = helpers.get('typeof');
t.isExpressionStatement(typeofHelper);
// true
```
Inside a plugin:
```js
export default {
visitor: {
UnaryExpression(path) {
// The .addHelper function adds, if needed, the helper to the file
// and returns an expression which references the helper
const typeofHelper = this.addHelper("typeof");
t.isExpression(typeofHelper); // true
}
};
```
## Defining Helpers
> **NOTE**: This package is only meant to be used by the packages inluded in this repository. There is currently no way for third-party plugins to define an helper.
Helpers are defined in the `src/helpers.js` file, and they must be valid modules which follow these guidelines:
- They must have a default export, which is their entry-point.
- They can import other helpers, exclusively by using default imports.
- They can't have named exports.
```js
helpers.customHelper = defineHelper(`
import dep from "dependency";
const foo = 2;
export default function getFooTimesDepPlusX(x) {
return foo * dep() + x;
}
`);
```
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