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bootstrap scripts should preload with low priority. This allows the browser to prefer loading paint blocking resources like images even if they arrive after the script preload has been processed
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7 files changed

+83
-24
lines changed

7 files changed

+83
-24
lines changed

‎packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js‎

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4245,6 +4245,8 @@ export function writePreamble(
42454245
// Flush unblocked stylesheets by precedence
42464246
resources.precedences.forEach(flushAllStylesInPreamble, destination);
42474247

4248+
resources.bootstrapScripts.forEach(flushResourceInPreamble, destination);
4249+
42484250
resources.scripts.forEach(flushResourceInPreamble, destination);
42494251
resources.scripts.clear();
42504252

@@ -4322,6 +4324,9 @@ export function writeHoistables(
43224324
// but we want to kick off preloading as soon as possible
43234325
resources.precedences.forEach(preloadLateStyles, destination);
43244326

4327+
// bootstrap scripts should flush above script priority but these can only flush in the preamble
4328+
// so we elide the code here for performance
4329+
43254330
resources.scripts.forEach(flushResourceLate, destination);
43264331
resources.scripts.clear();
43274332

@@ -4875,6 +4880,7 @@ export type Resources = {
48754880
// usedImagePreloads: Set<PreloadResource>,
48764881
precedences: Map<string, Set<StyleResource>>,
48774882
stylePrecedences: Map<string, StyleTagResource>,
4883+
bootstrapScripts: Set<PreloadResource>,
48784884
scripts: Set<ScriptResource>,
48794885
explicitStylesheetPreloads: Set<PreloadResource>,
48804886
// explicitImagePreloads: Set<PreloadResource>,
@@ -4901,6 +4907,7 @@ export function createResources(): Resources {
49014907
// usedImagePreloads: new Set(),
49024908
precedences: new Map(),
49034909
stylePrecedences: new Map(),
4910+
bootstrapScripts: new Set(),
49044911
scripts: new Set(),
49054912
explicitStylesheetPreloads: new Set(),
49064913
// explicitImagePreloads: new Set(),
@@ -5470,6 +5477,7 @@ function preloadBootstrapScript(
54705477
rel: 'preload',
54715478
href: src,
54725479
as: 'script',
5480+
fetchPriority: 'low',
54735481
nonce,
54745482
integrity,
54755483
crossOrigin,
@@ -5481,7 +5489,7 @@ function preloadBootstrapScript(
54815489
props,
54825490
};
54835491
resources.preloadsMap.set(key, resource);
5484-
resources.explicitScriptPreloads.add(resource);
5492+
resources.bootstrapScripts.add(resource);
54855493
pushLinkImpl(resource.chunks, props);
54865494
}
54875495

@@ -5511,6 +5519,7 @@ function preloadBootstrapModule(
55115519
const props: PreloadModuleProps = {
55125520
rel: 'modulepreload',
55135521
href: src,
5522+
fetchPriority: 'low',
55145523
nonce,
55155524
integrity,
55165525
crossOrigin,
@@ -5522,7 +5531,7 @@ function preloadBootstrapModule(
55225531
props,
55235532
};
55245533
resources.preloadsMap.set(key, resource);
5525-
resources.explicitScriptPreloads.add(resource);
5534+
resources.bootstrapScripts.add(resource);
55265535
pushLinkImpl(resource.chunks, props);
55275536
return;
55285537
}

‎packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js‎

Lines changed: 66 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -610,17 +610,30 @@ describe('ReactDOMFizzServer', () => {
610610
});
611611

612612
expect(getVisibleChildren(container)).toEqual([
613-
<link rel="preload" href="init.js" as="script" nonce={CSPnonce} />,
614613
<link
615614
rel="preload"
615+
fetchpriority="low"
616+
href="init.js"
617+
as="script"
618+
nonce={CSPnonce}
619+
/>,
620+
<link
621+
rel="preload"
622+
fetchpriority="low"
616623
href="init2.js"
617624
as="script"
618625
nonce={CSPnonce}
619626
integrity="init2hash"
620627
/>,
621-
<link rel="modulepreload" href="init.mjs" nonce={CSPnonce} />,
622628
<link
623629
rel="modulepreload"
630+
fetchpriority="low"
631+
href="init.mjs"
632+
nonce={CSPnonce}
633+
/>,
634+
<link
635+
rel="modulepreload"
636+
fetchpriority="low"
624637
href="init2.mjs"
625638
nonce={CSPnonce}
626639
integrity="init2hash"
@@ -640,17 +653,30 @@ describe('ReactDOMFizzServer', () => {
640653
resolve({default: Text});
641654
});
642655
expect(getVisibleChildren(container)).toEqual([
643-
<link rel="preload" href="init.js" as="script" nonce={CSPnonce} />,
644656
<link
645657
rel="preload"
658+
fetchpriority="low"
659+
href="init.js"
660+
as="script"
661+
nonce={CSPnonce}
662+
/>,
663+
<link
664+
rel="preload"
665+
fetchpriority="low"
646666
href="init2.js"
647667
as="script"
648668
nonce={CSPnonce}
649669
integrity="init2hash"
650670
/>,
651-
<link rel="modulepreload" href="init.mjs" nonce={CSPnonce} />,
652671
<link
653672
rel="modulepreload"
673+
fetchpriority="low"
674+
href="init.mjs"
675+
nonce={CSPnonce}
676+
/>,
677+
<link
678+
rel="modulepreload"
679+
fetchpriority="low"
654680
href="init2.mjs"
655681
nonce={CSPnonce}
656682
integrity="init2hash"
@@ -3797,12 +3823,23 @@ describe('ReactDOMFizzServer', () => {
37973823
expect(getVisibleChildren(document)).toEqual(
37983824
<html>
37993825
<head>
3800-
<link rel="preload" href="foo" as="script" />
3801-
<link rel="preload" href="bar" as="script" />
3802-
<link rel="preload" href="baz" as="script" integrity="qux" />
3803-
<link rel="modulepreload" href="quux" />
3804-
<link rel="modulepreload" href="corge" />
3805-
<link rel="modulepreload" href="grault" integrity="garply" />
3826+
<link rel="preload" fetchpriority="low" href="foo" as="script" />
3827+
<link rel="preload" fetchpriority="low" href="bar" as="script" />
3828+
<link
3829+
rel="preload"
3830+
fetchpriority="low"
3831+
href="baz"
3832+
as="script"
3833+
integrity="qux"
3834+
/>
3835+
<link rel="modulepreload" fetchpriority="low" href="quux" />
3836+
<link rel="modulepreload" fetchpriority="low" href="corge" />
3837+
<link
3838+
rel="modulepreload"
3839+
fetchpriority="low"
3840+
href="grault"
3841+
integrity="garply"
3842+
/>
38063843
</head>
38073844
<body>
38083845
<div>hello world</div>
@@ -3866,14 +3903,27 @@ describe('ReactDOMFizzServer', () => {
38663903
expect(getVisibleChildren(document)).toEqual(
38673904
<html>
38683905
<head>
3869-
<link rel="preload" href="foo" as="script" />
3870-
<link rel="preload" href="bar" as="script" />
3871-
<link rel="preload" href="baz" as="script" crossorigin="" />
3872-
<link rel="preload" href="qux" as="script" crossorigin="" />
3873-
<link rel="modulepreload" href="quux" />
3874-
<link rel="modulepreload" href="corge" />
3906+
<link rel="preload" fetchpriority="low" href="foo" as="script" />
3907+
<link rel="preload" fetchpriority="low" href="bar" as="script" />
3908+
<link
3909+
rel="preload"
3910+
fetchpriority="low"
3911+
href="baz"
3912+
as="script"
3913+
crossorigin=""
3914+
/>
3915+
<link
3916+
rel="preload"
3917+
fetchpriority="low"
3918+
href="qux"
3919+
as="script"
3920+
crossorigin=""
3921+
/>
3922+
<link rel="modulepreload" fetchpriority="low" href="quux" />
3923+
<link rel="modulepreload" fetchpriority="low" href="corge" />
38753924
<link
38763925
rel="modulepreload"
3926+
fetchpriority="low"
38773927
href="grault"
38783928
crossorigin="use-credentials"
38793929
/>

‎packages/react-dom/src/__tests__/ReactDOMFizzServerBrowser-test.js‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -84,7 +84,7 @@ describe('ReactDOMFizzServerBrowser', () => {
8484
);
8585
const result = await readResult(stream);
8686
expect(result).toMatchInlineSnapshot(
87-
`"<link rel="preload" href="init.js" as="script"/><link rel="modulepreload" href="init.mjs"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
87+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low"/><link rel="modulepreload" href="init.mjs" fetchPriority="low"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
8888
);
8989
});
9090

@@ -500,7 +500,7 @@ describe('ReactDOMFizzServerBrowser', () => {
500500
);
501501
const result = await readResult(stream);
502502
expect(result).toMatchInlineSnapshot(
503-
`"<link rel="preload" href="init.js" as="script" nonce="R4nd0m"/><link rel="modulepreload" href="init.mjs" nonce="R4nd0m"/><div>hello world</div><script nonce="${nonce}">INIT();</script><script src="init.js" nonce="${nonce}" async=""></script><script type="module" src="init.mjs" nonce="${nonce}" async=""></script>"`,
503+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low" nonce="R4nd0m"/><link rel="modulepreload" href="init.mjs" fetchPriority="low" nonce="R4nd0m"/><div>hello world</div><script nonce="${nonce}">INIT();</script><script src="init.js" nonce="${nonce}" async=""></script><script type="module" src="init.mjs" nonce="${nonce}" async=""></script>"`,
504504
);
505505
});
506506
});

‎packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -98,7 +98,7 @@ describe('ReactDOMFizzServerNode', () => {
9898
pipe(writable);
9999
jest.runAllTimers();
100100
expect(output.result).toMatchInlineSnapshot(
101-
`"<link rel="preload" href="init.js" as="script"/><link rel="modulepreload" href="init.mjs"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
101+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low"/><link rel="modulepreload" href="init.mjs" fetchPriority="low"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
102102
);
103103
});
104104

‎packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -84,7 +84,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
8484
});
8585
const prelude = await readContent(result.prelude);
8686
expect(prelude).toMatchInlineSnapshot(
87-
`"<link rel="preload" href="init.js" as="script"/><link rel="modulepreload" href="init.mjs"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
87+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low"/><link rel="modulepreload" href="init.mjs" fetchPriority="low"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
8888
);
8989
});
9090

‎packages/react-dom/src/__tests__/ReactDOMFizzStaticNode-test.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -86,7 +86,7 @@ describe('ReactDOMFizzStaticNode', () => {
8686
);
8787
const prelude = await readContent(result.prelude);
8888
expect(prelude).toMatchInlineSnapshot(
89-
`"<link rel="preload" href="init.js" as="script"/><link rel="modulepreload" href="init.mjs"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
89+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low"/><link rel="modulepreload" href="init.mjs" fetchPriority="low"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
9090
);
9191
});
9292

‎packages/react-server-dom-fb/src/__tests__/ReactDOMServerFB-test.internal.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -59,7 +59,7 @@ describe('ReactDOMServerFB', () => {
5959
});
6060
const result = readResult(stream);
6161
expect(result).toMatchInlineSnapshot(
62-
`"<link rel="preload" href="init.js" as="script"/><link rel="modulepreload" href="init.mjs"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
62+
`"<link rel="preload" href="init.js" as="script" fetchPriority="low"/><link rel="modulepreload" href="init.mjs" fetchPriority="low"/><div>hello world</div><script>INIT();</script><script src="init.js" async=""></script><script type="module" src="init.mjs" async=""></script>"`,
6363
);
6464
});
6565

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