How to import a CSS file using Rollup and output it as a string?
Apr 05, 2025 pm 07:03 PM
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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