How to remove imported css in reactjs

Question

I have used the following code to import css

componentWillMount() {
    import('./patient-summary.css');
}

How to remove imported css from react when component is not in use. When i go back to previous screen this css gets applied there. Any idea ?

UPDATE:: Webpack config

const path = require('path');
const webpack = require('webpack');

module.exports = {
  entry: './src/index.js',
  output: {
  filename: 'bundle.js',
  path: path.resolve(__dirname, 'public/dist')
},
module: {
  rules: [
      {
          test: /\.js?$/, 
          loader: 'babel-loader',
          exclude: /node_modules/
      },
      {
          test: /\.css$/,
          use: [ 'style-loader', 'css-loader' ]
      },
      {
        test: /\.(woff|woff2|eot|ttf|otf)$/,
        loader: "file-loader"
      }
      ,
      {
        test: /\.(png|jpeg|jpg|gif|svg)$/,
        loader: "file-loader"
      }
  ]
  },
  devServer: {
  contentBase: path.resolve(__dirname, "public"),
  historyApiFallback: true,
  port: 3000,
  watchOptions: {
    // Delay the rebuild after the first change
    aggregateTimeout: 300,

    // Poll using interval (in ms, accepts boolean too)
    poll: 1000,
  },
  },
  plugins: [
   // Ignore node_modules so CPU usage with poll
   // watching drops significantly.
   new webpack.WatchIgnorePlugin([
      path.join(__dirname, "node_modules")
   ])
 ],
 };

Answer 1

I found a (sort of) reasonable way to do this in React. In short, you can lazy-load React components that contain the import './style.css', and when it loads, you can capture the imported StyleSheet to toggle its StyleSheet.disabled property later.

Here's the main code, with more explanation below. Here's my Gist.

useDisableImportedStyles.tsx

import { useEffect } from 'react'

// global list of all the StyleSheets that are touched in useDisableImportedStyles
const switchableGlobalStyleSheets: StyleSheet[] = []

// just to clarify what createUseDisableImportedStyles() returns
type useDisableImportedStyles = () => void

export const createUseDisableImportedStyles = (
    immediatelyUnloadStyle: boolean = true
    // if true: immediately unloads the StyleSheet when the component is unmounted
    // if false: waits to unloads the StyleSheet until another instance of useDisableImportedStyles is called.This avoids a flash of unstyled content
): useDisableImportedStyles => {
    let localStyleSheet: StyleSheet
    return () => {
        useEffect(() => {

            // if there are no stylesheets, you did something wrong...
            if (document.styleSheets.length < 1) return

            // set the localStyleSheet if this is the first time this instance of this useEffect is called
            if (localStyleSheet == null) {
                localStyleSheet = document.styleSheets[document.styleSheets.length - 1]
                switchableGlobalStyleSheets.push(localStyleSheet)
            }

            // if we are switching StyleSheets, disable all switchableGlobalStyleSheets
            if (!immediatelyUnloadStyle) {
                switchableGlobalStyleSheets.forEach(styleSheet => styleSheet.disabled = true)
            }

            // enable our StyleSheet!
            localStyleSheet.disabled = false

            // if we are NOT switching StyleSheets, disable this StyleSheet when the component is unmounted
            if (immediatelyUnloadStyle) return () => {
                if (localStyleSheet != null) localStyleSheet.disabled = true
            }

        })
    }
}

WARNING: This is pretty finicky. You must set this up exactly or there may be unintended consequences

Conditions:

1. createUseDisableImportedStyles must called in global scope in the same tsx file as the imported css being targeted and the component to be lazy loaded

import React from 'react'
import { createUseDisableImportedStyles } from './useDisableImportedStyles'
import './global-styles.css'
const useDisableImportedStyles = createUseDisableImportedStyles()
export const CssComponent: React.FC<{}> = () => {
    useDisableImportedStyles()
    return null
}
export default CssComponent

2. A component using this hook should be lazy loaded:

LazyCssComponent = React.lazy(() => import('./cssComponent'))
...
<React.Suspense fallback={<></>}>
    {condition && <LazyCssComponent/>}
</React.Suspense>

3. An exception to lazy loading might be using this in a single, normal, non-lazy component so styles are loaded on first render

• NOTE: the InitialCssComponent never needs to actually render, it just needs to be imported
• BUT: this will only work if there is one single .css file imported globally, otherwise, I don't know what would happen

import InitialCssComponent  from './initialCssComponent'
LazyCssComponent = React.lazy(() => import('./cssComponent'))
//...
{false && <InitialCssComponent/>}
<React.Suspense fallback={<></>}>
    {condition && <LazyCssComponent/>}
</React.Suspense>

GOOD LUCK!

Answer 2

First of all, AFAIK, you should not call any imports in componentWillMount. This means that every time a new component about to mount, this css will be loaded over and over. Instead, it must be placed at the beginning of your module.

The way that you avoid unnecessary css imports is to avoid unnecessary component imports. Hence, if your component is not called anywhere, then this css will not be loaded.

For routing, I think you will need to do some code splitting, but I am not sure if it is straightforward or the right way to do.

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