When working with Rollup.js, a popular module bundler for JavaScript, you may often encounter the need to import external dependencies or third-party libraries. Rollup.js provides several ways to handle these dependencies efficiently. In this article, we will explore different techniques for importing external modules and libraries in your Rollup.js project.

1. Installing External Dependencies

Before you can import and use external libraries in your Rollup.js project, you need to install them as dependencies. You can do this using npm or yarn, which are package managers commonly used in JavaScript projects.

For example, let’s say we want to use the lodash library in our project. To install it via npm, open your terminal and run:

npm install lodash

This will download and install lodash as a dependency in your project.

2. Using ES6 Import Statements

Once you have installed the external library, you can import it in your Rollup.js code using ES6 import statements.

import _ from 'lodash'; // import the entire lodash library
import { debounce } from 'lodash'; // import a specific function from lodash

Rollup.js will automatically analyze these import statements and bundle only the necessary parts of the library into your final bundle.

3. Configuring Rollup.js

To ensure that Rollup.js can resolve and bundle external dependencies correctly, you need to configure your Rollup.js configuration file.

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';

export default {
  // Your other Rollup.js configuration options...
  
  plugins: [
    // Other plugins...
    resolve(),
  ],
};

The rollup-plugin-node-resolve plugin helps Rollup.js resolve dependencies installed via npm or yarn. By including this plugin in your configuration, Rollup.js will be able to find and bundle external dependencies correctly.

4. Handling CommonJS Modules

Sometimes, you may encounter external dependencies that use a CommonJS module format (require and module.exports) instead of the ES6 module format (import and export). To handle such dependencies, you can use the rollup-plugin-commonjs plugin.

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';

export default {
  // Your other Rollup.js configuration options...
  
  plugins: [
    // Other plugins...
    resolve(),
    commonjs(),
  ],
};

By including the rollup-plugin-commonjs plugin, Rollup.js will be able to convert CommonJS modules to the ES6 module format, making them compatible with Rollup.js.

Conclusion

Rollup.js provides convenient ways to handle external dependencies in your JavaScript projects. By following the steps outlined in this article, you can efficiently import and bundle third-party libraries and modules using Rollup.js. Remember to install the dependencies, configure Rollup.js correctly, and use the appropriate import statements to make the best use of external code in your projects.

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