How to configure in Rollup that will generate only single output file from multiple input files?

Configuring Rollup to handle multiple input files and produce a single output file can primarily be achieved by using the @rollup/plugin-virtual plugin. This approach allows us to create a virtual 'entry point' from multiple source files, where we import all required modules. Rollup then processes these modules to generate a single bundled output file.

The following provides a step-by-step guide and example demonstrating how to implement this:

1. Install the necessary plugins

First, install Rollup and @rollup/plugin-virtual. You can install these packages using npm:

bash
npm install rollup @rollup/plugin-virtual --save-dev

2. Configure Rollup

Next, configure Rollup in your rollup.config.js file. Here is an example configuration for generating a single output file from multiple input files:

javascript
// Import the virtual plugin
import virtual from '@rollup/plugin-virtual';

export default {
  // Create a virtual entry file using the virtual plugin
  input: 'virtual-entry',
  plugins: [
    virtual({
      'virtual-entry': `
        // Import your module files here
        import './src/module1.js';
        import './src/module2.js';
        // Continue importing additional modules as needed
      `
    })
  ],
  output: {
    file: 'bundle.js', // Path and name of the output file
    format: 'iife' // Output format, using an immediately-invoked function expression
  }
};

3. Explanation of the code

In the above configuration, we create a virtual entry file named virtual-entry. Within this virtual file, we import all modules that need to be bundled. The @rollup/plugin-virtual plugin processes this virtual entry, and Rollup analyzes and bundles these modules to generate the specified single output file.

4. Run Rollup

Finally, you can run Rollup and generate the bundled file using the following command:

bash
npx rollup -c

This will generate the bundle.js file based on the configuration in rollup.config.js.

Summary

By using the @rollup/plugin-virtual plugin, we can flexibly configure Rollup to generate a single output file from multiple module files. This method is very useful when you need to combine multiple scattered modules into a single library or application.