Convert exports to server components

- `ScriptElement` renders the script only if it has not been rendered onto the DOM already. It does this by using  the prop `isGlobal` and a serverside variable. This removes the need for React Context entirely
- `Balancer` is now partially serverside, rendering its script and `ClientBalancer`. Any code that doesn't explicitly have to run on the client was moved to the server

Author: Andrew Wiggin

src/client.tsx

@@ -0,0 +1,155 @@
+'use client'
+
+import React from 'react'
+import {SYMBOL_KEY, SYMBOL_OBSERVER_KEY} from './constants'
+import type {BalancerProps} from "./index";
+
+declare global {
+    interface Window {
+        [SYMBOL_KEY]: RelayoutFn
+    }
+}
+
+export interface WrapperElement extends HTMLElement {
+    [SYMBOL_OBSERVER_KEY]?: ResizeObserver | undefined
+}
+
+type RelayoutFn = (
+    id: string | number,
+    ratio: number,
+    wrapper?: WrapperElement
+) => void
+
+export const relayout: RelayoutFn = (id, ratio, wrapper) => {
+    wrapper =
+        wrapper || document.querySelector<WrapperElement>(`[data-br="${id}"]`)
+    const container = wrapper.parentElement
+
+    const update = (width: number) => (wrapper.style.maxWidth = width + 'px')
+
+    // Reset wrapper width
+    wrapper.style.maxWidth = ''
+
+    // Get the initial container size
+    const width = container.clientWidth
+    const height = container.clientHeight
+
+    // Synchronously do binary search and calculate the layout
+    let lower: number = width / 2 - 0.25
+    let upper: number = width + 0.5
+    let middle: number
+
+    if (width) {
+        while (lower + 1 < upper) {
+            middle = Math.round((lower + upper) / 2)
+            update(middle)
+            if (container.clientHeight === height) {
+                upper = middle
+            } else {
+                lower = middle
+            }
+        }
+
+        // Update the wrapper width
+        update(upper * ratio + width * (1 - ratio))
+    }
+
+    // Create a new observer if we don't have one.
+    // Note that we must inline the key here as we use `toString()` to serialize
+    // the function.
+    if (!wrapper['__wrap_o']) {
+        ;(wrapper['__wrap_o'] = new ResizeObserver(() => {
+            self.__wrap_b(0, +wrapper.dataset.brr, wrapper)
+        })).observe(container)
+    }
+}
+
+export const RELAYOUT_STR = relayout.toString()
+
+const IS_SERVER = typeof window === 'undefined'
+const useIsomorphicLayoutEffect = IS_SERVER
+    ? React.useEffect
+    : React.useLayoutEffect
+
+interface ClientBalancerProps extends BalancerProps {
+    id: string
+    // `as` and `ratio` are required in the client component
+    as: BalancerProps['as'],
+    ratio: BalancerProps['ratio'],
+}
+export const ClientBalancer: React.FC<ClientBalancerProps> = ({
+                                                                  id,
+                                                                as: Wrapper,
+                                                                ratio,
+                                                                children,
+                                                                ...props
+                                                            }) => {
+    const wrapperRef = React.useRef<WrapperElement>()
+
+    // Re-balance on content change and on mount/hydration.
+    useIsomorphicLayoutEffect(() => {
+        if (wrapperRef.current) {
+            // Re-assign the function here as the component can be dynamically rendered, and script tag won't work in that case.
+            ;(self[SYMBOL_KEY] = relayout)(0, ratio, wrapperRef.current)
+        }
+    }, [children, ratio])
+
+    // Remove the observer when unmounting.
+    useIsomorphicLayoutEffect(() => {
+        return () => {
+            if (!wrapperRef.current) return
+
+            const resizeObserver = wrapperRef.current[SYMBOL_OBSERVER_KEY]
+            if (!resizeObserver) return
+
+            resizeObserver.disconnect()
+            delete wrapperRef.current[SYMBOL_OBSERVER_KEY]
+        }
+    }, [])
+
+    return (
+        <>
+            <Wrapper
+                {...props}
+                data-br={id}
+                data-brr={ratio}
+                ref={wrapperRef}
+                style={{
+                    display: 'inline-block',
+                    verticalAlign: 'top',
+                    textDecoration: 'inherit',
+                }}
+                suppressHydrationWarning
+            >
+                {children}
+            </Wrapper>
+        </>
+    )
+}
+
+// As Next.js adds `display: none` to `body` for development, we need to trigger
+// a re-balance right after the style is removed, synchronously.
+if (!IS_SERVER && process.env.NODE_ENV !== 'production') {
+    const next_dev_style = document.querySelector<HTMLElement>(
+        '[data-next-hide-fouc]'
+    )
+    if (next_dev_style) {
+        const callback: MutationCallback = (mutationList) => {
+            for (const mutation of mutationList) {
+                for (const node of Array.from(mutation.removedNodes)) {
+                    if (node !== next_dev_style) continue
+
+                    observer.disconnect()
+                    const elements =
+                        document.querySelectorAll<WrapperElement>('[data-br]')
+
+                    for (const element of Array.from(elements)) {
+                        self[SYMBOL_KEY](0, +element.dataset.brr, element)
+                    }
+                }
+            }
+        }
+        const observer = new MutationObserver(callback)
+        observer.observe(document.head, {childList: true})
+    }
+}

src/constants.ts

@@ -0,0 +1,2 @@
+export const SYMBOL_KEY = '__wrap_b'
+export const SYMBOL_OBSERVER_KEY = '__wrap_o'