Reduce bundle size on the server (#4464)

2026-09-17 08:05:19 +00:00 · 2026-08-12 13:22:51 +02:00
parent 7594a334d8
commit 65f99eafe5
19 changed files with 751 additions and 117 deletions
@@ -0,0 +1,8 @@
+---
+"@gitbook/react-openapi": major
+"gitbook": patch
+---
+
+Lazy load the Scalar API client modal and stop preloading the Scalar runtime. The modal is now code-split into its own chunk, fetched in parallel with the runtime only when a reader clicks "Test it", and a spinner is shown on the button until the client opens.
+
+Breaking: the package no longer ships the modal in its main entry — consumers must serve the emitted `ScalarApiModal` chunk and use a bundler that supports dynamic `import()`, and the Scalar runtime is no longer preloaded on page load. The internal `preloadScalarRuntime` helper is removed.
@@ -125,19 +125,21 @@
    },
    "scripts": {
        "generate": "./scripts/generate.sh",
-        "clean": "rm -rf ./.next && rm -rf ./public/~gitbook/static/icons && rm -rf ./public/~gitbook/static/math",
-        "dev": "env-cmd --silent -f ../../.env.local next --webpack",
-        "build": "next build --webpack",
-        "build:local": "GITBOOK_URL=http://localhost:3000 next build --webpack",
+        "generate:assets": "bun ./scripts/generate-mermaid-runtime.ts && bun ./scripts/generate-scalar-runtime.ts",
+        "clean": "rm -rf ./.next && rm -rf ./public/~gitbook/static/icons && rm -rf ./public/~gitbook/static/math && rm -rf ./public/~gitbook/static/mermaid && rm -rf ./public/~gitbook/static/scalar",
+        "dev": "bun run generate:assets && env-cmd --silent -f ../../.env.local next --webpack",
+        "build": "bun run generate:assets && next build --webpack",
+        "build:local": "bun run generate:assets && GITBOOK_URL=http://localhost:3000 next build --webpack",
        "check:css-browser-compatibility": "bun scripts/check-css-browser-compatibility.ts",
        "start": "GITBOOK_URL=http://localhost:3000 next start",
-        "build:cloudflare": "GITBOOK_RUNTIME=cloudflare opennextjs-cloudflare build",
+        "build:cloudflare": "bun run generate:assets && GITBOOK_RUNTIME=cloudflare opennextjs-cloudflare build",
        "dev:cloudflare": "wrangler dev --port 8771 --env preview",
        "dev:cf:middleware": "wrangler dev --port 8771 --inspector-port 9230 --env dev --config ./openNext/customWorkers/middlewareWrangler.jsonc",
        "dev:cf:server": "wrangler dev --port 8772 --env dev --config ./openNext/customWorkers/defaultWrangler.jsonc",
+        "profile:cf:memory": "bun run build:cloudflare && bun ./scripts/profile-opennext-memory.ts",
        "e2e": "playwright test e2e/internal.spec.ts e2e/cookie-banner.spec.ts e2e/pdf.spec.ts e2e/select.spec.ts --project=chromium",
        "e2e-customers": "playwright test e2e/customers.spec.ts --project=chromium",
-        "unit": "bun test {src,packages} --preload ./tests/preload-bun.ts",
+        "unit": "bun run generate:assets && bun test {src,packages} --preload ./tests/preload-bun.ts",
        "e2e-browserless": "bun test ./tests/",
        "typecheck": "tsc --noEmit"
    },
@@ -7,3 +7,5 @@ rm -rf ./.next
 rm -rf ./public/~gitbook/static/icons
 rm -rf ./public/~gitbook/static/math
 rm -rf ./public/~gitbook/static/embed
+rm -rf ./public/~gitbook/static/mermaid
+rm -rf ./public/~gitbook/static/scalar
@@ -0,0 +1,44 @@
+import { mkdir, rename, rm } from 'node:fs/promises';
+import { createRequire } from 'node:module';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { build } from 'bun';
+
+import { MERMAID_RUNTIME_PATH } from '../src/components/DocumentView/CodeBlock/mermaid-runtime-path';
+
+const scriptDir = dirname(fileURLToPath(import.meta.url));
+const outputDir = join(scriptDir, '../public/~gitbook/static/mermaid');
+const temporaryDir = join(outputDir, '.build');
+const require = createRequire(import.meta.url);
+const mermaidPackage = require('mermaid/package.json') as { version: string };
+const zenumlPackage = require('@mermaid-js/mermaid-zenuml/package.json') as { version: string };
+
+// The runtime URL is served as immutable, it has to change whenever the bundled versions change.
+if (
+    MERMAID_RUNTIME_PATH !==
+    `mermaid/mermaid@${mermaidPackage.version}-zenuml@${zenumlPackage.version}.mjs`
+) {
+    throw new Error(
+        'Update MERMAID_RUNTIME_PATH for the installed mermaid and @mermaid-js/mermaid-zenuml versions'
+    );
+}
+
+await rm(outputDir, { force: true, recursive: true });
+await mkdir(temporaryDir, { recursive: true });
+
+const result = await build({
+    entrypoints: [join(scriptDir, 'mermaid-runtime.ts')],
+    format: 'esm',
+    minify: true,
+    outdir: temporaryDir,
+    target: 'browser',
+});
+
+const [output] = result.outputs;
+if (!result.success || !output || result.outputs.length !== 1) {
+    throw new Error(`Unable to build Mermaid runtime: ${result.logs.join('\n')}`);
+}
+
+const outputPath = join(outputDir, MERMAID_RUNTIME_PATH.replace('mermaid/', ''));
+await rename(output.path, outputPath);
+await rm(temporaryDir, { force: true, recursive: true });
@@ -0,0 +1,81 @@
+import { mkdir, rename, rm } from 'node:fs/promises';
+import { createRequire } from 'node:module';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { build } from 'bun';
+
+import { SCALAR_RUNTIME_PATH } from '../src/components/DocumentView/OpenAPI/scalar-runtime-path';
+
+const scriptDir = dirname(fileURLToPath(import.meta.url));
+const outputDir = join(scriptDir, '../public/~gitbook/static/scalar');
+const temporaryDir = join(outputDir, '.build');
+const scalarPackage = createRequire(import.meta.url)('@scalar/api-client-react/package.json') as {
+    version: string;
+};
+
+if (SCALAR_RUNTIME_PATH !== `scalar/scalar-api-client@${scalarPackage.version}.mjs`) {
+    throw new Error(
+        'Update SCALAR_RUNTIME_PATH for the installed @scalar/api-client-react version'
+    );
+}
+
+const reactShim = `
+const react = () => globalThis.__gitbookScalarReact;
+export const createContext = (...args) => react().createContext(...args);
+export const useContext = (...args) => react().useContext(...args);
+export const useEffect = (...args) => react().useEffect(...args);
+export const useRef = (...args) => react().useRef(...args);
+export const useSyncExternalStore = (...args) => react().useSyncExternalStore(...args);
+`;
+
+const jsxRuntimeShim = `
+const runtime = () => globalThis.__gitbookScalarJSXRuntime;
+export const jsx = (...args) => runtime().jsx(...args);
+export const jsxs = (...args) => runtime().jsxs(...args);
+`;
+
+await rm(outputDir, { force: true, recursive: true });
+await mkdir(temporaryDir, { recursive: true });
+
+const result = await build({
+    entrypoints: [join(scriptDir, 'scalar-runtime.ts')],
+    format: 'esm',
+    minify: true,
+    outdir: temporaryDir,
+    plugins: [
+        {
+            name: 'scalar-react-shims',
+            setup(build) {
+                build.onResolve({ filter: /^react$/ }, () => ({
+                    namespace: 'scalar-runtime',
+                    path: 'react',
+                }));
+                build.onResolve({ filter: /^react\/jsx-runtime$/ }, () => ({
+                    namespace: 'scalar-runtime',
+                    path: 'react-jsx-runtime',
+                }));
+                build.onLoad({ filter: /^react$/, namespace: 'scalar-runtime' }, () => ({
+                    contents: reactShim,
+                    loader: 'js',
+                }));
+                build.onLoad(
+                    { filter: /^react-jsx-runtime$/, namespace: 'scalar-runtime' },
+                    () => ({
+                        contents: jsxRuntimeShim,
+                        loader: 'js',
+                    })
+                );
+            },
+        },
+    ],
+    target: 'browser',
+});
+
+const [output] = result.outputs;
+if (!result.success || !output || result.outputs.length !== 1) {
+    throw new Error(`Unable to build Scalar runtime: ${result.logs.join('\n')}`);
+}
+
+const outputPath = join(outputDir, SCALAR_RUNTIME_PATH.replace('scalar/', ''));
+await rename(output.path, outputPath);
+await rm(temporaryDir, { force: true, recursive: true });
@@ -3,6 +3,9 @@
 set -o errexit
 set -o pipefail

+# Generate assets that the server loads by URL instead of bundling.
+bun run generate:assets
+
 # Copy the assets
 gitbook-icons ./public/~gitbook/static/icons custom-icons
 gitbook-math ./public/~gitbook/static/math
@@ -0,0 +1,16 @@
+import zenuml from '@mermaid-js/mermaid-zenuml';
+import mermaid from 'mermaid';
+
+let registration: Promise<void> | null = null;
+
+export async function loadMermaid() {
+    if (!registration) {
+        registration = mermaid.registerExternalDiagrams([zenuml]).catch((error) => {
+            registration = null;
+            throw error;
+        });
+    }
+
+    await registration;
+    return mermaid;
+}
@@ -0,0 +1,306 @@
+import { stat } from 'node:fs/promises';
+import { createConnection } from 'node:net';
+import { join } from 'node:path';
+import { file, sleep, spawn } from 'bun';
+import WebSocket from 'ws';
+
+type HeapUsage = {
+    usedSize: number;
+    totalSize: number;
+    embedderHeapUsedSize: number;
+    backingStorageSize: number;
+};
+
+type DevWorker = {
+    command: string[];
+    process: WorkerProcess;
+};
+
+type WorkerProcess = {
+    exitCode: number | null;
+    exited: Promise<number>;
+    stdin: { write(data: string): unknown };
+    kill(): void;
+};
+
+const appPath = `${import.meta.dir}/..`;
+const requestURL = process.env.PROFILE_URL ?? 'http://127.0.0.1:8771/url/gitbook.com/docs';
+const requestCount = Number.parseInt(process.env.PROFILE_REQUESTS ?? '20', 10);
+const forceGarbageCollection = process.env.PROFILE_FORCE_GC === 'true';
+const settleMs = Number.parseInt(process.env.PROFILE_SETTLE_MS ?? '5000', 10);
+
+if (
+    !Number.isSafeInteger(requestCount) ||
+    requestCount < 1 ||
+    !Number.isSafeInteger(settleMs) ||
+    settleMs < 0
+) {
+    throw new Error('PROFILE_REQUESTS and PROFILE_SETTLE_MS must be positive integers');
+}
+
+const workers: DevWorker[] = [];
+
+try {
+    const server = await startWorker(['bun', 'run', 'dev:cf:server'], 8772);
+    workers.push(server);
+    const middleware = await startWorker(['bun', 'run', 'dev:cf:middleware'], 8771);
+    workers.push(middleware);
+
+    const coldResponse = await requestUntilReady(requestURL);
+    await maybeCollectGarbage();
+
+    const cold = await getMeasurements();
+    const responses = await Promise.all(
+        Array.from({ length: requestCount }, () => request(requestURL))
+    );
+
+    await sleep(settleMs);
+    await maybeCollectGarbage();
+
+    const afterLoad = await getMeasurements();
+    const bundle = await getBundleMetrics();
+
+    // biome-ignore lint/suspicious/noConsole: JSON on stdout is this script's public interface.
+    console.log(
+        JSON.stringify(
+            {
+                requestURL,
+                requestCount,
+                forceGarbageCollection,
+                settleMs,
+                coldResponse,
+                responses: summarizeResponses(responses),
+                heap: { cold, afterLoad },
+                bundle,
+            },
+            null,
+            2
+        )
+    );
+} finally {
+    for (const worker of workers.reverse()) {
+        await stopWorker(worker.process);
+    }
+}
+
+async function startWorker(command: string[], port: number): Promise<DevWorker> {
+    const process = spawn(command, {
+        cwd: appPath,
+        stdin: 'pipe',
+        stdout: 'ignore',
+        stderr: 'ignore',
+    });
+
+    try {
+        await waitForPort(port, process);
+        return { command, process };
+    } catch (error) {
+        process.kill();
+        await process.exited;
+        throw error;
+    }
+}
+
+async function stopWorker(process: WorkerProcess) {
+    process.stdin.write('x\n');
+    await Promise.race([process.exited, sleep(5_000)]);
+
+    if (process.exitCode === null) {
+        process.kill();
+        await process.exited;
+    }
+}
+
+async function waitForPort(port: number, process: WorkerProcess) {
+    const timeout = Date.now() + 60_000;
+
+    while (Date.now() < timeout) {
+        if (process.exitCode !== null) {
+            throw new Error(`Worker exited before becoming ready: ${process.exitCode}`);
+        }
+
+        try {
+            await connectToPort(port);
+            return;
+        } catch {
+            await sleep(250);
+        }
+    }
+
+    throw new Error(`Worker did not become ready within 60 seconds on port ${port}`);
+}
+
+async function connectToPort(port: number) {
+    await new Promise<void>((resolve, reject) => {
+        const socket = createConnection({ host: '127.0.0.1', port });
+        socket.once('connect', () => {
+            socket.destroy();
+            resolve();
+        });
+        socket.once('error', (error) => {
+            socket.destroy();
+            reject(error);
+        });
+    });
+}
+
+async function request(url: string) {
+    const startedAt = performance.now();
+    const response = await fetch(url);
+    const body = await response.arrayBuffer();
+
+    return {
+        status: response.status,
+        bytes: body.byteLength,
+        durationMs: Math.round(performance.now() - startedAt),
+    };
+}
+
+async function requestUntilReady(url: string) {
+    let response: Awaited<ReturnType<typeof request>> | undefined;
+
+    for (let attempt = 0; attempt < 20; attempt += 1) {
+        response = await request(url);
+        if (response.status < 500) {
+            return response;
+        }
+        await sleep(250);
+    }
+
+    throw new Error(`Worker did not return a successful response: ${response?.status}`);
+}
+
+function summarizeResponses(responses: Awaited<ReturnType<typeof request>>[]) {
+    return {
+        statuses: Object.fromEntries(
+            Object.entries(Object.groupBy(responses, ({ status }) => status)).map(
+                ([status, groupedResponses]) => [status, groupedResponses?.length ?? 0]
+            )
+        ),
+        bytes: responses.reduce((total, { bytes }) => total + bytes, 0),
+        maxDurationMs: Math.max(...responses.map(({ durationMs }) => durationMs)),
+    };
+}
+
+async function getMeasurements() {
+    return {
+        server: await sendDevtoolsCommand<HeapUsage>(
+            'ws://127.0.0.1:9229/ws',
+            'Runtime.getHeapUsage'
+        ),
+        middleware: await sendDevtoolsCommand<HeapUsage>(
+            'ws://127.0.0.1:9230/ws',
+            'Runtime.getHeapUsage'
+        ),
+    };
+}
+
+async function maybeCollectGarbage() {
+    if (!forceGarbageCollection) {
+        return;
+    }
+
+    await Promise.all([
+        collectGarbage('ws://127.0.0.1:9229/ws'),
+        collectGarbage('ws://127.0.0.1:9230/ws'),
+    ]);
+}
+
+async function collectGarbage(url: string) {
+    await new Promise<void>((resolve, reject) => {
+        const websocket = new WebSocket(url);
+        const timeout = setTimeout(() => {
+            websocket.terminate();
+            reject(new Error('Timed out waiting for HeapProfiler.takeHeapSnapshot'));
+        }, 60_000);
+
+        websocket.on('open', () => {
+            websocket.send(
+                JSON.stringify({
+                    id: 1,
+                    method: 'HeapProfiler.takeHeapSnapshot',
+                    params: { reportProgress: false },
+                })
+            );
+        });
+        websocket.on('message', (data) => {
+            const message = JSON.parse(data.toString());
+            if (message.id !== 1) {
+                return;
+            }
+
+            clearTimeout(timeout);
+            websocket.terminate();
+            if (message.error) {
+                reject(new Error(message.error.message));
+                return;
+            }
+            resolve();
+        });
+        websocket.on('error', () => {
+            clearTimeout(timeout);
+            reject(new Error(`Unable to connect to DevTools: ${url}`));
+        });
+    });
+}
+
+async function sendDevtoolsCommand<Result>(url: string, method: string): Promise<Result> {
+    return new Promise<Result>((resolve, reject) => {
+        const websocket = new WebSocket(url);
+        const timeout = setTimeout(() => {
+            websocket.terminate();
+            reject(new Error(`Timed out waiting for ${method}`));
+        }, 10_000);
+
+        websocket.on('open', () => {
+            websocket.send(JSON.stringify({ id: 1, method }));
+        });
+        websocket.on('message', (data) => {
+            const message = JSON.parse(data.toString());
+            if (message.id !== 1) {
+                return;
+            }
+
+            clearTimeout(timeout);
+            websocket.terminate();
+            if (message.error) {
+                reject(new Error(message.error.message));
+                return;
+            }
+            resolve(message.result as Result);
+        });
+        websocket.on('error', () => {
+            clearTimeout(timeout);
+            reject(new Error(`Unable to connect to DevTools: ${url}`));
+        });
+    });
+}
+
+async function getBundleMetrics() {
+    const handlerPath = join(
+        appPath,
+        '.open-next/server-functions/default/packages/gitbook/handler.mjs'
+    );
+    const metafilePath = `${handlerPath}.meta.json`;
+    const metafile = (await file(metafilePath).json()) as {
+        outputs: Record<string, { inputs: Record<string, { bytesInOutput: number }> }>;
+    };
+    const [outputPath] = Object.keys(metafile.outputs);
+    if (!outputPath) {
+        throw new Error(`No output found in metafile: ${metafilePath}`);
+    }
+    const output = metafile.outputs[outputPath];
+    if (!output) {
+        throw new Error(`Missing output in metafile: ${outputPath}`);
+    }
+    const shikiBytes = Object.entries(output.inputs).reduce(
+        (total, [path, input]) =>
+            path.includes('@shikijs/langs') ? total + input.bytesInOutput : total,
+        0
+    );
+
+    return {
+        handlerBytes: (await stat(handlerPath)).size,
+        shikiLanguageBytes: shikiBytes,
+    };
+}
@@ -0,0 +1 @@
+export { ApiClientModalProvider, useApiClientModal } from '@scalar/api-client-react';
@@ -6,6 +6,7 @@ import type {
    SiteCustomizationSettings,
 } from '@gitbook/api';

+import { getAssetURL } from '@/lib/assets';
 import { getNodeFragmentByType } from '@/lib/document';

 import type { BlockProps } from '../Block';
@@ -15,6 +16,7 @@ import { CodeBlockRenderer } from './CodeBlockRenderer';
 import { MermaidCodeBlockLazy } from './MermaidCodeBlockLazy';
 import { highlight } from './highlight';
 import { type RenderedInline, getInlines } from './highlight-tokens';
+import { MERMAID_RUNTIME_PATH } from './mermaid-runtime-path';

 /**
 * Render a code block, can be client-side or server-side.
@@ -118,7 +120,10 @@ export async function CodeBlock(
    return (
        <React.Suspense fallback={null}>
            {isMermaid ? (
-                <MermaidCodeBlockLazy {...clientProps} />
+                <MermaidCodeBlockLazy
+                    {...clientProps}
+                    mermaidRuntimeURL={getAssetURL(MERMAID_RUNTIME_PATH)}
+                />
            ) : (
                <ClientCodeBlock {...clientProps} />
            )}
@@ -20,8 +20,12 @@ const DIALOG_ANIMATION_MS = 200;
 /**
 * Used to render a Mermaid diagram from a CodeBlock.
 */
-export function MermaidCodeBlock(props: ClientBlockProps) {
-    const { block, mode, style } = props;
+export function MermaidCodeBlock(
+    props: ClientBlockProps & {
+        mermaidRuntimeURL: string;
+    }
+) {
+    const { block, mode, style, mermaidRuntimeURL } = props;
    const source = getPlainCodeBlock(block);
    const rootRef = useRef<HTMLDivElement>(null);
    const panelRef = useRef<HTMLDivElement>(null);
@@ -80,6 +84,7 @@ export function MermaidCodeBlock(props: ClientBlockProps) {
                    source,
                    id,
                    darkMode,
+                    mermaidRuntimeURL,
                });
            })
                .then((result) => {
@@ -116,7 +121,7 @@ export function MermaidCodeBlock(props: ClientBlockProps) {
            cleanupPanZoom?.();
            setPanZoom(null);
        };
-    }, [source, id, darkMode, shouldRender]);
+    }, [source, id, darkMode, mermaidRuntimeURL, shouldRender]);

    // Lock the page scroll while the dialog is on screen (handles scrollbar width and iOS).
    usePreventScroll({ isDisabled: !isPresent });
@@ -286,9 +291,10 @@ async function renderMermaidDiagram(args: {
    source: string;
    id: string;
    darkMode: boolean;
+    mermaidRuntimeURL: string;
 }): Promise<RenderResult> {
-    const { source, id, darkMode } = args;
-    const { mermaid } = await loadMermaid();
+    const { source, id, darkMode, mermaidRuntimeURL } = args;
+    const { mermaid } = await loadMermaid(mermaidRuntimeURL);

    mermaid.initialize({
        startOnLoad: false,
@@ -338,13 +344,16 @@ let mermaidLoadPromise: Promise<{
    mermaid: typeof import('mermaid')['default'];
 }> | null = null;

-async function loadMermaid() {
+async function loadMermaid(runtimeURL: string) {
    if (!mermaidLoadPromise) {
-        mermaidLoadPromise = Promise.all([import('mermaid'), import('@mermaid-js/mermaid-zenuml')])
-            .then(async ([{ default: mermaid }, { default: zenuml }]) => {
-                await mermaid.registerExternalDiagrams([zenuml]);
-                return { mermaid };
-            })
+        mermaidLoadPromise = import(/* webpackIgnore: true */ runtimeURL)
+            .then(
+                async (runtime: {
+                    loadMermaid: () => Promise<typeof import('mermaid')['default']>;
+                }) => {
+                    return { mermaid: await runtime.loadMermaid() };
+                }
+            )
            .catch((error) => {
                mermaidLoadPromise = null;
                throw error;
@@ -10,6 +10,6 @@ const MermaidCodeBlock = dynamic(
    { ssr: true }
 );

-export function MermaidCodeBlockLazy(props: ClientBlockProps) {
+export function MermaidCodeBlockLazy(props: ClientBlockProps & { mermaidRuntimeURL: string }) {
    return <MermaidCodeBlock {...props} />;
 }
@@ -0,0 +1 @@
+export const MERMAID_RUNTIME_PATH = 'mermaid/mermaid@11.14.0-zenuml@0.2.2.mjs';
@@ -9,6 +9,7 @@ import { Heading } from '../Heading';

 import './style.css';
 import { DEFAULT_LOCALE, getSpaceLocale } from '@/intl/server';
+import { getAssetURL } from '@/lib/assets';
 import type { GitBookAnyContext } from '@/lib/context';
 import { GITBOOK_URL } from '@/lib/env';
 import { buildSignedProxyUrl } from '@/lib/openapi/proxy-token';
@@ -17,6 +18,7 @@ import type {
    OpenAPISchemasBlock,
    OpenAPIWebhookBlock,
 } from '@/lib/openapi/types';
+import { SCALAR_RUNTIME_PATH } from './scalar-runtime-path';

 // Serve the proxy from GitBook's own origin rather than the customer domain, so a proxied
 // response can never execute as HTML under a customer's trusted origin.
@@ -113,6 +115,7 @@ export function getOpenAPIContext(args: {
        expandAllResponses: expandAllResponses || props.context.mode === 'print',
        expandAllModelSections: expandAllModelSections || props.context.mode === 'print',
        headless,
+        scalarRuntimeURL: getAssetURL(SCALAR_RUNTIME_PATH),
        id: block.meta?.id,
        blockKey: block.key,
        locale,
@@ -0,0 +1 @@
+export const SCALAR_RUNTIME_PATH = 'scalar/scalar-api-client@1.3.46.mjs';
@@ -284,6 +284,11 @@ body {
    @apply size-2.5;
 }

+/* Same size as the play icon it replaces, so the button doesn't shift while loading. */
+.scalar-activate-button .scalar-activate-spinner {
+    @apply animate-spin motion-reduce:animate-none;
+}
+
 .scalar-app-loading {
    flex: 1;
    display: flex;
@@ -1,16 +1,27 @@
 'use client';

-import { ApiClientModalProvider, useApiClientModal } from '@scalar/api-client-react';
-import { Suspense, useEffect, useImperativeHandle, useMemo, useRef, useState } from 'react';
+import * as React from 'react';
+import { type ComponentType, useRef, useState } from 'react';
 import { createPortal } from 'react-dom';
+import * as ReactJSXRuntime from 'react/jsx-runtime';

 import type { OpenAPIV3_1 } from '@gitbook/openapi-parser';
-import { useOpenAPIOperationContext } from './OpenAPIOperationContext';
-import { useOpenAPIPrefillContext } from './OpenAPIPrefillContextProvider';
+import type {
+    ScalarApiModalProps,
+    ScalarModalControllerRef,
+    ScalarRuntime,
+} from './ScalarApiModal';
 import type { OpenAPIClientContext } from './context';
 import { t } from './translate';
 import type { OpenAPIOperationData } from './types';
-import { resolveTryItPrefillForOperation } from './util/tryit-prefill';
+
+let scalarRuntimePromise: Promise<ScalarRuntime> | null = null;
+
+/** Everything needed to render the client, none of it in the initial bundle. */
+type ScalarClient = {
+    runtime: ScalarRuntime;
+    Modal: ComponentType<ScalarApiModalProps>;
+};

 /**
 * Button which launches the Scalar API Client
@@ -26,121 +37,113 @@ export function ScalarApiButton(props: {
 }) {
    const { method, path, securities, servers, specUrl, withProxy, context } = props;
    const [isOpen, setIsOpen] = useState(false);
+    const [isLoading, setIsLoading] = useState(false);
+    const [client, setClient] = useState<ScalarClient | null>(null);
    const controllerRef = useRef<ScalarModalControllerRef>(null);

    return (
        <div className="scalar scalar-activate">
            <button
+                type="button"
                className="scalar-activate-button button"
+                aria-busy={isLoading}
                onClick={() => {
                    controllerRef.current?.openClient?.();
                    setIsOpen(true);
+                    if (!client) {
+                        setIsLoading(true);
+                        loadScalarClient(context.scalarRuntimeURL)
+                            .then(setClient)
+                            .catch((error) => {
+                                console.error('Unable to load the Scalar API client', error);
+                                setIsOpen(false);
+                                setIsLoading(false);
+                            });
+                    }
                }}
            >
                {t(context.translation, 'test_it')}
-                <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 10 12" fill="currentColor">
-                    <path
-                        stroke="currentColor"
-                        strokeWidth="1.5"
-                        d="M1 10.05V1.43c0-.2.2-.31.37-.22l7.26 4.08c.17.1.17.33.01.43l-7.26 4.54a.25.25 0 0 1-.38-.21Z"
-                    />
-                </svg>
+                {isLoading ? (
+                    <svg
+                        className="scalar-activate-spinner"
+                        aria-hidden="true"
+                        xmlns="http://www.w3.org/2000/svg"
+                        viewBox="0 0 24 24"
+                        fill="none"
+                    >
+                        <circle
+                            cx="12"
+                            cy="12"
+                            r="10"
+                            stroke="currentColor"
+                            strokeOpacity="0.3"
+                            strokeWidth="3"
+                        />
+                        <path
+                            d="M12 2a10 10 0 0 1 10 10"
+                            stroke="currentColor"
+                            strokeWidth="3"
+                            strokeLinecap="round"
+                        />
+                    </svg>
+                ) : (
+                    <svg
+                        aria-hidden="true"
+                        xmlns="http://www.w3.org/2000/svg"
+                        viewBox="0 0 10 12"
+                        fill="currentColor"
+                    >
+                        <path
+                            stroke="currentColor"
+                            strokeWidth="1.5"
+                            d="M1 10.05V1.43c0-.2.2-.31.37-.22l7.26 4.08c.17.1.17.33.01.43l-7.26 4.54a.25.25 0 0 1-.38-.21Z"
+                        />
+                    </svg>
+                )}
            </button>

            {isOpen &&
+                client &&
                createPortal(
-                    <Suspense fallback={null}>
-                        <ScalarModal
-                            controllerRef={controllerRef}
-                            withProxy={withProxy}
-                            proxyUrl={context.proxyUrl}
-                            method={method}
-                            path={path}
-                            securities={securities}
-                            servers={servers}
-                            specUrl={specUrl}
-                        />
-                    </Suspense>,
+                    <client.Modal
+                        controllerRef={controllerRef}
+                        method={method}
+                        path={path}
+                        securities={securities}
+                        servers={servers}
+                        specUrl={specUrl}
+                        withProxy={withProxy}
+                        context={context}
+                        runtime={client.runtime}
+                        onReady={() => setIsLoading(false)}
+                    />,
                    document.body
                )}
        </div>
    );
 }

-function ScalarModal(props: {
-    method: OpenAPIV3_1.HttpMethods;
-    path: string;
-    securities: OpenAPIOperationData['securities'];
-    servers: OpenAPIOperationData['servers'];
-    specUrl: string;
-    withProxy: boolean;
-    proxyUrl?: string;
-    controllerRef: React.Ref<ScalarModalControllerRef>;
-}) {
-    const { method, path, securities, servers, specUrl, withProxy, proxyUrl, controllerRef } =
-        props;
+/** Fetch the modal chunk and the Scalar runtime in parallel. */
+async function loadScalarClient(runtimeURL: string): Promise<ScalarClient> {
+    const [runtime, mod] = await Promise.all([
+        loadScalarRuntime(runtimeURL),
+        import('./ScalarApiModal'),
+    ]);

-    const getPrefillInputContextData = useOpenAPIPrefillContext();
-    const prefillInputContext = getPrefillInputContextData();
-
-    const prefillConfig = resolveTryItPrefillForOperation({
-        operation: { securities, servers },
-        prefillInputContext,
-    });
-
-    return (
-        <ApiClientModalProvider
-            configuration={{
-                url: specUrl,
-                ...prefillConfig,
-                proxyUrl: withProxy ? proxyUrl : undefined,
-            }}
-            initialRequest={{ method: toScalarHttpMethod(method), path }}
-        >
-            <ScalarModalController method={method} path={path} controllerRef={controllerRef} />
-        </ApiClientModalProvider>
-    );
+    return { runtime, Modal: mod.ScalarApiModal };
 }

-function toScalarHttpMethod<T extends OpenAPIV3_1.HttpMethods>(method: T): Uppercase<T> {
-    return method.toUpperCase() as Uppercase<T>;
-}
-
-type ScalarModalControllerRef = {
-    openClient: (() => void) | undefined;
-};
-
-function ScalarModalController(props: {
-    method: OpenAPIV3_1.HttpMethods;
-    path: string;
-    controllerRef: React.Ref<ScalarModalControllerRef>;
-}) {
-    const { method, path, controllerRef } = props;
-    const client = useApiClientModal();
-    const openScalarClient = client?.open;
-    const { onOpenClient: trackClientOpening } = useOpenAPIOperationContext();
-    const openClient = useMemo(() => {
-        if (openScalarClient) {
-            return () => {
-                openScalarClient({
-                    method: toScalarHttpMethod(method),
-                    path,
-                    _source: 'gitbook',
-                });
-                trackClientOpening({ method, path });
-            };
-        }
-        return null;
-    }, [openScalarClient, method, path, trackClientOpening]);
-    useImperativeHandle(
-        controllerRef,
-        () => ({ openClient: openClient ? () => openClient() : undefined }),
-        [openClient]
-    );
-
-    // Open at mount
-    useEffect(() => {
-        openClient?.();
-    }, [openClient]);
-    return null;
+async function loadScalarRuntime(runtimeURL: string): Promise<ScalarRuntime> {
+    if (!scalarRuntimePromise) {
+        Object.assign(globalThis, {
+            __gitbookScalarReact: React,
+            __gitbookScalarJSXRuntime: ReactJSXRuntime,
+        });
+        scalarRuntimePromise = import(/* webpackIgnore: true */ runtimeURL).catch((error) => {
+            scalarRuntimePromise = null;
+            throw error;
+        });
+    }
+
+    return scalarRuntimePromise;
 }
@@ -0,0 +1,137 @@
+'use client';
+
+import {
+    type ComponentType,
+    type ReactNode,
+    type Ref,
+    useEffect,
+    useImperativeHandle,
+    useMemo,
+    useRef,
+} from 'react';
+
+import type { OpenAPIV3_1 } from '@gitbook/openapi-parser';
+import { useOpenAPIOperationContext } from './OpenAPIOperationContext';
+import { useOpenAPIPrefillContext } from './OpenAPIPrefillContextProvider';
+import type { OpenAPIClientContext } from './context';
+import type { OpenAPIOperationData } from './types';
+import { resolveTryItPrefillForOperation } from './util/tryit-prefill';
+
+export type ScalarModalControllerRef = {
+    openClient: (() => void) | undefined;
+};
+
+export type ScalarRuntime = {
+    ApiClientModalProvider: ComponentType<{
+        configuration: object;
+        initialRequest: { method: string; path: string };
+        children: ReactNode;
+    }>;
+    useApiClientModal: () => {
+        open?: (request: { method: string; path: string; _source?: string }) => void;
+    } | null;
+};
+
+export type ScalarApiModalProps = {
+    method: OpenAPIV3_1.HttpMethods;
+    path: string;
+    securities: OpenAPIOperationData['securities'];
+    servers: OpenAPIOperationData['servers'];
+    specUrl: string;
+    withProxy: boolean;
+    context: OpenAPIClientContext;
+    runtime: ScalarRuntime;
+    controllerRef: Ref<ScalarModalControllerRef>;
+    /** Called once the client is initialized and the modal is opening. */
+    onReady: () => void;
+};
+
+/** Loaded only after a reader opens the Try it client. */
+export function ScalarApiModal(props: ScalarApiModalProps) {
+    const {
+        method,
+        path,
+        securities,
+        servers,
+        specUrl,
+        withProxy,
+        context,
+        controllerRef,
+        runtime,
+        onReady,
+    } = props;
+    const getPrefillInputContextData = useOpenAPIPrefillContext();
+    const prefillInputContext = getPrefillInputContextData();
+
+    const prefillConfig = resolveTryItPrefillForOperation({
+        operation: { securities, servers },
+        prefillInputContext,
+    });
+
+    return (
+        <runtime.ApiClientModalProvider
+            configuration={{
+                url: specUrl,
+                ...prefillConfig,
+                proxyUrl: withProxy ? context.proxyUrl : undefined,
+            }}
+            initialRequest={{ method: toScalarHttpMethod(method), path }}
+        >
+            <ScalarModalController
+                method={method}
+                path={path}
+                controllerRef={controllerRef}
+                runtime={runtime}
+                onReady={onReady}
+            />
+        </runtime.ApiClientModalProvider>
+    );
+}
+
+function ScalarModalController(props: {
+    method: OpenAPIV3_1.HttpMethods;
+    path: string;
+    controllerRef: Ref<ScalarModalControllerRef>;
+    runtime: ScalarRuntime;
+    onReady: () => void;
+}) {
+    const { method, path, controllerRef, runtime, onReady } = props;
+    const client = runtime.useApiClientModal();
+    const openScalarClient = client?.open;
+    const { onOpenClient: trackClientOpening } = useOpenAPIOperationContext();
+    const openClient = useMemo(() => {
+        if (openScalarClient) {
+            return () => {
+                openScalarClient({
+                    method: toScalarHttpMethod(method),
+                    path,
+                    _source: 'gitbook',
+                });
+                trackClientOpening({ method, path });
+            };
+        }
+        return null;
+    }, [openScalarClient, method, path, trackClientOpening]);
+    useImperativeHandle(
+        controllerRef,
+        () => ({ openClient: openClient ? () => openClient() : undefined }),
+        [openClient]
+    );
+
+    // Through a ref, so an unstable callback doesn't re-open the client on every render.
+    const onReadyRef = useRef(onReady);
+    onReadyRef.current = onReady;
+
+    useEffect(() => {
+        if (openClient) {
+            openClient();
+            onReadyRef.current();
+        }
+    }, [openClient]);
+
+    return null;
+}
+
+function toScalarHttpMethod<T extends OpenAPIV3_1.HttpMethods>(method: T): Uppercase<T> {
+    return method.toUpperCase() as Uppercase<T>;
+}
@@ -47,6 +47,9 @@ export interface OpenAPIClientContext {
     */
    proxyUrl?: string;

+    /** URL of the lazily loaded Scalar browser runtime. */
+    scalarRuntimeURL: string;
+
    /**
     * Mark the context as a client context.
     */
@@ -54,7 +57,7 @@ export interface OpenAPIClientContext {
 }

 export interface OpenAPIContext
-    extends Omit<OpenAPIClientContext, '$$isClientContext$$' | 'proxyUrl'> {
+    extends Omit<OpenAPIClientContext, '$$isClientContext$$' | 'proxyUrl' | 'scalarRuntimeURL'> {
    /**
     * Render a code block.
     */
@@ -90,6 +93,9 @@ export interface OpenAPIContext
     * Called at render time (server-side) with the server origins for an operation.
     */
    resolveProxyUrl?: (allowedOrigins: string[]) => string | null;
+
+    /** URL of the lazily loaded Scalar browser runtime. */
+    scalarRuntimeURL: string;
 }

 export type OpenAPIUniversalContext = OpenAPIClientContext | OpenAPIContext;
@@ -125,6 +131,7 @@ export function getOpenAPIClientContext(context: OpenAPIUniversalContext): OpenA
        blockKey: context.blockKey,
        id: context.id,
        proxyUrl: '$$isClientContext$$' in context ? context.proxyUrl : undefined,
+        scalarRuntimeURL: context.scalarRuntimeURL,
        $$isClientContext$$: true,
    };
 }
				`@@ -0,0 +1 @@`
				`export { ApiClientModalProvider, useApiClientModal } from '@scalar/api-client-react';`
				`@@ -0,0 +1 @@`
				`export const MERMAID_RUNTIME_PATH = 'mermaid/mermaid@11.14.0-zenuml@0.2.2.mjs';`
				`@@ -0,0 +1 @@`
				`export const SCALAR_RUNTIME_PATH = 'scalar/scalar-api-client@1.3.46.mjs';`