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index.tsx
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index.tsx
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import React, {
Fragment,
createContext,
useCallback,
useContext,
useEffect,
useState,
useMemo,
memo
} from 'react'
import type { UseThemeProps, ThemeProviderProps } from './types'
const colorSchemes = ['light', 'dark']
const MEDIA = '(prefers-color-scheme: dark)'
const isServer = typeof window === 'undefined'
const ThemeContext = createContext<UseThemeProps | undefined>(undefined)
const defaultContext: UseThemeProps = { setTheme: _ => {}, themes: [] }
export const useTheme = () => useContext(ThemeContext) ?? defaultContext
export const ThemeProvider: React.FC<ThemeProviderProps> = props => {
const context = useContext(ThemeContext)
// Ignore nested context providers, just passthrough children
if (context) return <Fragment>{props.children}</Fragment>
return <Theme {...props} />
}
const defaultThemes = ['light', 'dark'];
const Theme: React.FC<ThemeProviderProps> = ({
forcedTheme,
disableTransitionOnChange = false,
enableSystem = true,
enableColorScheme = true,
storageKey = 'theme',
themes = defaultThemes,
defaultTheme = enableSystem ? 'system' : 'light',
attribute = 'data-theme',
value,
children,
nonce
}) => {
const [theme, setThemeState] = useState(() => getTheme(storageKey, defaultTheme))
const [resolvedTheme, setResolvedTheme] = useState(() => getTheme(storageKey))
const attrs = !value ? themes : Object.values(value)
const applyTheme = useCallback(theme => {
let resolved = theme
if (!resolved) return
// If theme is system, resolve it before setting theme
if (theme === 'system' && enableSystem) {
resolved = getSystemTheme()
}
const name = value ? value[resolved] : resolved
const enable = disableTransitionOnChange ? disableAnimation() : null
const d = document.documentElement
if (attribute === 'class') {
d.classList.remove(...attrs)
if (name) d.classList.add(name)
} else {
if (name) {
d.setAttribute(attribute, name)
} else {
d.removeAttribute(attribute)
}
}
if (enableColorScheme) {
const fallback = colorSchemes.includes(defaultTheme) ? defaultTheme : null
const colorScheme = colorSchemes.includes(resolved) ? resolved : fallback
// @ts-ignore
d.style.colorScheme = colorScheme
}
enable?.()
}, [])
const setTheme = useCallback(
theme => {
setThemeState(theme)
// Save to storage
try {
localStorage.setItem(storageKey, theme)
} catch (e) {
// Unsupported
}
},
[forcedTheme]
)
const handleMediaQuery = useCallback(
(e: MediaQueryListEvent | MediaQueryList) => {
const resolved = getSystemTheme(e)
setResolvedTheme(resolved)
if (theme === 'system' && enableSystem && !forcedTheme) {
applyTheme('system')
}
},
[theme, forcedTheme]
)
// Always listen to System preference
useEffect(() => {
const media = window.matchMedia(MEDIA)
// Intentionally use deprecated listener methods to support iOS & old browsers
media.addListener(handleMediaQuery)
handleMediaQuery(media)
return () => media.removeListener(handleMediaQuery)
}, [handleMediaQuery])
// localStorage event handling
useEffect(() => {
const handleStorage = (e: StorageEvent) => {
if (e.key !== storageKey) {
return
}
// If default theme set, use it if localstorage === null (happens on local storage manual deletion)
const theme = e.newValue || defaultTheme
setTheme(theme)
}
window.addEventListener('storage', handleStorage)
return () => window.removeEventListener('storage', handleStorage)
}, [setTheme])
// Whenever theme or forcedTheme changes, apply it
useEffect(() => {
applyTheme(forcedTheme ?? theme)
}, [forcedTheme, theme])
const providerValue = useMemo(() => ({
theme,
setTheme,
forcedTheme,
resolvedTheme: theme === 'system' ? resolvedTheme : theme,
themes: enableSystem ? [...themes, 'system'] : themes,
systemTheme: (enableSystem ? resolvedTheme : undefined) as 'light' | 'dark' | undefined
}), [theme, setTheme, forcedTheme, resolvedTheme, enableSystem, themes]);
return (
<ThemeContext.Provider
value={providerValue}
>
<ThemeScript
{...{
forcedTheme,
disableTransitionOnChange,
enableSystem,
enableColorScheme,
storageKey,
themes,
defaultTheme,
attribute,
value,
children,
attrs,
nonce
}}
/>
{children}
</ThemeContext.Provider>
)
}
const ThemeScript = memo(
({
forcedTheme,
storageKey,
attribute,
enableSystem,
enableColorScheme,
defaultTheme,
value,
attrs,
nonce
}: ThemeProviderProps & { attrs: string[]; defaultTheme: string }) => {
const defaultSystem = defaultTheme === 'system'
// Code-golfing the amount of characters in the script
const optimization = (() => {
if (attribute === 'class') {
const removeClasses = `c.remove(${attrs.map((t: string) => `'${t}'`).join(',')})`
return `var d=document.documentElement,c=d.classList;${removeClasses};`
} else {
return `var d=document.documentElement,n='${attribute}',s='setAttribute';`
}
})()
const fallbackColorScheme = (() => {
if (!enableColorScheme) {
return ''
}
const fallback = colorSchemes.includes(defaultTheme) ? defaultTheme : null
if (fallback) {
return `if(e==='light'||e==='dark'||!e)d.style.colorScheme=e||'${defaultTheme}'`
} else {
return `if(e==='light'||e==='dark')d.style.colorScheme=e`
}
})()
const updateDOM = (name: string, literal: boolean = false, setColorScheme = true) => {
const resolvedName = value ? value[name] : name
const val = literal ? name + `|| ''` : `'${resolvedName}'`
let text = ''
// MUCH faster to set colorScheme alongside HTML attribute/class
// as it only incurs 1 style recalculation rather than 2
// This can save over 250ms of work for pages with big DOM
if (enableColorScheme && setColorScheme && !literal && colorSchemes.includes(name)) {
text += `d.style.colorScheme = '${name}';`
}
if (attribute === 'class') {
if (literal || resolvedName) {
text += `c.add(${val})`
} else {
text += `null`
}
} else {
if (resolvedName) {
text += `d[s](n,${val})`
}
}
return text
}
const scriptSrc = (() => {
if (forcedTheme) {
return `!function(){${optimization}${updateDOM(forcedTheme)}}()`
}
if (enableSystem) {
return `!function(){try{${optimization}var e=localStorage.getItem('${storageKey}');if(e==='system'${defaultSystem ? '||!e' : ''}){var t='${MEDIA}',m=window.matchMedia(t),x=t!==m.media||m.matches?'dark':'light';${updateDOM('x',true)}}else if(e){${
value ? `var x=${JSON.stringify(value)};` : ''
}${updateDOM(value ? `x[e]` : 'e', true)}}${
!defaultSystem ? `else{` + updateDOM(defaultTheme, false, false) + '}' : ''
}${fallbackColorScheme}}catch(e){}}()`
}
return `!function(){try{${optimization}var e=localStorage.getItem('${storageKey}');if(e){${
value ? `var x=${JSON.stringify(value)};` : ''
}${updateDOM(value ? `x[e]` : 'e', true)}}else{${updateDOM(
defaultTheme,
false,
false
)};}${fallbackColorScheme}}catch(t){}}();`
})()
return <script nonce={nonce} dangerouslySetInnerHTML={{ __html: scriptSrc }} />
},
// Never re-render this component
() => true
)
// Helpers
const getTheme = (key: string, fallback?: string) => {
if (isServer) return undefined
let theme
try {
theme = localStorage.getItem(key) || undefined
} catch (e) {
// Unsupported
}
return theme || fallback
}
const disableAnimation = () => {
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)
return () => {
// Force restyle
;(() => window.getComputedStyle(document.body))()
// Wait for next tick before removing
setTimeout(() => {
document.head.removeChild(css)
}, 1)
}
}
const getSystemTheme = (e?: MediaQueryList | MediaQueryListEvent) => {
if (!e) e = window.matchMedia(MEDIA)
const isDark = e.matches
const systemTheme = isDark ? 'dark' : 'light'
return systemTheme
}