Extract transition code in a separate hook. Add documentation.

README.md

@@ -133,6 +133,8 @@ Let's dig into the details.
 - `specifiedTheme`: The theme from the session storage.
 - `themeAction`: The action name used to change the theme in the session
   storage.
+- `disableTransitionOnThemeChange`: Disable CSS transitions on theme change to
+  prevent the flashing effect.
 
 ### useTheme
 

packages/remix-themes-app/app/root.tsx

@@ -57,7 +57,11 @@ function App() {
 export default function AppWithProviders() {
   const data = useLoaderData()
   return (
-    <ThemeProvider specifiedTheme={data.theme} themeAction="/action/set-theme">
+    <ThemeProvider
+      specifiedTheme={data.theme}
+      themeAction="/action/set-theme"
+      disableTransitionOnThemeChange={true}
+    >
       <App />
     </ThemeProvider>
   )

packages/remix-themes-app/app/styles/index.css

@@ -1,19 +1,23 @@
 [data-theme='dark'] {
   background-color: #000;
   color: white;
+  transition: background-color 2s ease;
 }
 
 [data-theme='light'] {
   background-color: #f2f2f2;
   color: black;
+  transition: background-color 2s ease;
 }
 
 .dark {
   background-color: #000;
   color: white;
+  transition: background-color 2s ease;
 }
 
 .light {
   background-color: #f2f2f2;
   color: black;
+  transition: background-color 2s ease;
 }

packages/remix-themes/src/theme-provider.tsx

@@ -1,6 +1,7 @@
 import type {Dispatch, ReactNode, SetStateAction} from 'react'
 import {createContext, useState, useContext, useEffect, useRef} from 'react'
 import {useBroadcastChannel} from './useBroadcastChannel'
+import {useCorrectCssTransition} from './useCorrectCssTransition'
 
 export enum Theme {
   DARK = 'dark',
@@ -15,6 +16,7 @@ const ThemeContext = createContext<ThemeContextType | undefined>(undefined)
 ThemeContext.displayName = 'ThemeContext'
 
 const prefersLightMQ = '(prefers-color-scheme: light)'
+
 const getPreferredTheme = () =>
   window.matchMedia(prefersLightMQ).matches ? Theme.LIGHT : Theme.DARK
 
@@ -34,6 +36,10 @@ export function ThemeProvider({
   themeAction,
   disableTransitionOnThemeChange = false,
 }: ThemeProviderProps) {
+  const ensureCorrectTransition = useCorrectCssTransition({
+    disableTransitions: disableTransitionOnThemeChange,
+  })
+
   const [theme, setTheme] = useState<Theme | null>(() => {
     // On the server, if we don't have a specified theme then we should
     // return null and the clientThemeCode will set the theme for us
@@ -52,31 +58,11 @@ export function ThemeProvider({
 
   const mountRun = useRef(false)
 
-  const broadcastThemeChange = useBroadcastChannel('remix-themes', e =>
-    setTheme(e.data),
-  )
-
-  const disableTransition = () => {
-    const style = document.createElement('style')
-
-    style.textContent = `
-      * {
-          -ms-transition: none!important;
-          -webkit-transition: none!important;
-          -moz-transition: none!important;
-          -o-transition: none!important;
-          transition: none!important
-      }
-    `
-
-    document.head.appendChild(style);
-
-    (() => window.getComputedStyle(document.body))();
-
-    setTimeout(() => {
-      document.head.removeChild(style);
-    }, 1);
-  }
+  const broadcastThemeChange = useBroadcastChannel('remix-themes', e => {
+    ensureCorrectTransition(() => {
+      setTheme(e.data)
+    })
+  })
 
   useEffect(() => {
     if (!mountRun.current) {
@@ -90,18 +76,20 @@ export function ThemeProvider({
       body: JSON.stringify({theme}),
     })
 
-    broadcastThemeChange(theme)
-    disableTransitionOnThemeChange && disableTransition()
-  }, [broadcastThemeChange, disableTransitionOnThemeChange, theme, themeAction])
+    ensureCorrectTransition(() => {
+      broadcastThemeChange(theme)
+    })
+  }, [broadcastThemeChange, theme, themeAction, ensureCorrectTransition])
 
   useEffect(() => {
     const handleChange = (ev: MediaQueryListEvent) => {
-      setTheme(ev.matches ? Theme.LIGHT : Theme.DARK)
-      disableTransitionOnThemeChange && disableTransition()
+      ensureCorrectTransition(() => {
+        setTheme(ev.matches ? Theme.LIGHT : Theme.DARK)
+      })
     }
     mediaQuery?.addEventListener('change', handleChange)
     return () => mediaQuery?.removeEventListener('change', handleChange)
-  }, [])
+  }, [ensureCorrectTransition])
 
   return (
     <ThemeContext.Provider value={[theme, setTheme]}>

packages/remix-themes/src/useCorrectCssTransition.ts

@@ -0,0 +1,43 @@
+import {useCallback} from 'react'
+
+function withoutTransition(callback: Function) {
+  const css = document.createElement('style')
+  css.appendChild(
+    document.createTextNode(
+      `* {
+       -webkit-transition: none !important;
+       -moz-transition: none !important;
+       -o-transition: none !important;
+       -ms-transition: none !important;
+       transition: none !important;
+    }`,
+    ),
+  )
+  document.head.appendChild(css)
+
+  callback()
+
+  setTimeout(() => {
+    // Calling getComputedStyle forces the browser to redraw
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    const _ = window.getComputedStyle(css).transition
+    document.head.removeChild(css)
+  }, 0)
+}
+
+export function useCorrectCssTransition({
+  disableTransitions = false,
+}: {disableTransitions?: boolean} = {}) {
+  return useCallback(
+    (callback: Function) => {
+      if (disableTransitions) {
+        withoutTransition(() => {
+          callback()
+        })
+      } else {
+        callback()
+      }
+    },
+    [disableTransitions],
+  )
+}

yarn.lock

@@ -1514,7 +1514,7 @@
     source-map-support "^0.5.21"
     stream-slice "^0.1.2"
 
-"@remix-run/react@latest":
+"@remix-run/react@1.12.0", "@remix-run/react@latest":
   version "1.12.0"
   resolved "https://registry.yarnpkg.com/@remix-run/react/-/react-1.12.0.tgz#7ad27e7d152b0980ef09ac851f849cc445a9e51f"
   integrity sha512-BokbMOILGJvUvwOsTXAUrucvfFz/SBKVgSHke2+89DZIU7H2Z1UWe5t8wRTfjQnfnSH2tAXCF0QxmVpo1GQ3dg==
@@ -1538,7 +1538,7 @@
     express "^4.17.1"
     morgan "^1.10.0"
 
-"@remix-run/[email protected]", "@remix-run/server-runtime@latest":
+"@remix-run/[email protected]":
   version "1.12.0"
   resolved "https://registry.yarnpkg.com/@remix-run/server-runtime/-/server-runtime-1.12.0.tgz#a2072c2e88b948b2a657993574cad01d42cf8cd4"
   integrity sha512-7I0165Ns/ffPfCEfuiqD58lMderTn2s/sew1xJ34ONa21mG/7+5T7diHIgxKST8rS3816JPmlwSqUaHgwbmO6Q==