How to import a CSS file using Rollup and output it as a string?

Rollup: Gracefully import and output CSS strings

When building projects with Rollup, handling CSS files often requires some additional configuration. This article describes how to use Rollup to import a CSS file and output its contents as strings into JavaScript code.

Challenge: Limitations of Direct Importing CSS

Importing CSS files directly into JavaScript modules (for example, import './styles.css' ) will cause Rollup errors, prompting that plug-ins are needed to handle non-JavaScript files. This is because Rollup only processes JavaScript modules by default.

Workaround: Use rollup-plugin-import-css

rollup-plugin-import-css plugin can solve this problem. It allows you to import CSS files and inject CSS code as strings into your JavaScript module.

Step 1: Install the plug-in

Use npm or yarn to install the plugin:

 npm install rollup-plugin-import-css --save-dev

Step 2: Configure Rollup

In your rollup.config.js (or similar configuration file), import and configure rollup-plugin-import-css plugin:

 import importCss from 'rollup-plugin-import-css';

export default {
  input: 'index.ts',
  output: {
    file: 'bundle.js',
    format: 'cjs' // or other formats you need},
  plugins: [
    importCss()
  ]
};

Step 3: Import CSS in the code

Now you can import the CSS file in your JavaScript code and use its contents as a string:

 import styles from './styles.css';

console.log({ styles }); // styles now contain CSS string

Step 4: Build the project

Run the Rollup build command (for example, rollup -c ). The styles variable will contain the contents of the styles.css file as a string.

Through the above steps, you can easily import and output CSS files in your Rollup project and output as strings, making it easier to dynamically process CSS code at runtime. Remember to select the appropriate output format ( format option) according to your project requirements.

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