# @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; } `); ```