Question

Technologies:

javascript

html

css

Tolerim

18 hours ago

How can WebPack be utilized to dynamically load CSS?

To create a single-page web app where the user can change the CSS theme using Webpack, I have added two buttons in the HTML code for testing purposes:

In the JavaScript code, I import the necessary CSS file when each button is clicked. However, Webpack returns an error stating that "import" statements should be at the top level. I have researched this issue but the suggested solutions do not work for me. To load CSS dynamically with Webpack, one option is to use the mini-css-extract-plugin. This extracts the CSS into a separate file and adds it to the HTML using a link tag. Then, I can dynamically load the appropriate CSS file when each button is clicked, like this:


import './assets/css/style.css';

const link = document.createElement('link');
link.type = 'text/css';
link.rel = 'stylesheet';
link.href = './assets/css/themes/light.css'; // default theme

document.head.appendChild(link);

document.getElementById('dark').addEventListener('click', () => {
  link.href = './assets/css/themes/dark.css';
});

document.getElementById('light').addEventListener('click', () => {
  link.href = './assets/css/themes/light.css';
});

This code adds a link tag to the head of the HTML, with the href pointing to the default theme (light.css). Then, when each button is clicked, the href is updated to point to the appropriate CSS file (dark.css or light.css).

Answers(1)

Accepted Answer

Yes, you cannot use ES6 import statements dynamically in this way because they must be used at the top level. One way to handle dynamic CSS loading with Webpack is to use the mini-css-extract-plugin, which allows you to extract CSS into separate files. You can then use the HtmlWebpackPlugin to dynamically inject the appropriate CSS file into your HTML file at runtime. First, install the necessary plugins by running npm install --save-dev mini-css-extract-plugin html-webpack-plugin. Then, update your webpack configuration to use the mini-css-extract-plugin to extract your CSS files into a separate file:

const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ MiniCssExtractPlugin.loader, 'css-loader' ]
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin()
  ]
}

Here, we're telling Webpack to use the MiniCssExtractPlugin to extract our CSS files into a separate file, and then use the Css-loader to apply CSS to our HTML. Next, you can create two separate CSS files for your light and dark themes and place them in a themes folder. For example, light.css would look like this:

body {
  background-color: white;
  color: black;
}

And dark.css would look like this:

body {
  background-color: black;
  color: white;
}

Then, in your JS file, you can use the HtmlWebpackPlugin to dynamically inject the appropriate CSS file when a theme button is clicked:

import './assets/css/style.css';
import { createTheme } from './assets/js/theme.js';
import * as lightTheme from './assets/css/themes/light.css';
import * as darkTheme from './assets/css/themes/dark.css';
import { merge } from 'lodash';

const themes = {
  light: lightTheme,
  dark: darkTheme
};

document.getElementById('dark').addEventListener('click', () => {
  applyTheme(themes.dark);
})

document.getElementById('light').addEventListener('click', () => {
  applyTheme(themes.light);
})

function applyTheme(theme) {
  const existingStyle = document.getElementById('dynamic-styles');

  if (existingStyle) {
    existingStyle.innerHTML = theme._getCss();
  } else {
    const newStyle = document.createElement('style');
    newStyle.setAttribute('id', 'dynamic-styles');
    newStyle.innerHTML = theme._getCss();
    document.head.appendChild(newStyle);
  }
}

createTheme(themes.light);

Here, we're using the lightTheme and darkTheme CSS files and storing them in an object. When a button is clicked, we call the applyTheme function, which dynamically injects the appropriate CSS into the page using the createTheme function. The createTheme function takes a theme as an argument and uses it to create a new stylesheet element with the specified CSS. Finally, you can update your index.html file to include the correct CSS file on load:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <link rel="stylesheet" href="./assets/css/style.css">
</head>
<body>
  <button id="dark">Dark</button>
  <button id="light">Light</button>
</body>
</html>

Here, we're including our main style.css file and relying on the dynamic CSS injection to include the appropriate theme CSS at runtime. Note that mini-css-extract-plugin does not support dynamic CSS loading out of the box. Therefore, we are using a slightly different approach here where we are inserting